The Monkey Orb of Asia

Just a quick entry for this week. And for the second week in a row, today's post will somehow involve monkeys.

Female monkey orb-weaving spider Neoscona punctigera, copyright Akio Tanikawa.

The orb-weavers of the family Araneidae are a highly diverse group of spiders, with well over 3000 known species. They are also one of the most familiar spider groups, often being relatively large as well as visible due to their construction of exposed and characteristic webs. The lady in the picture above represents one of the more moderately sized species, being about a centimetre in length (Tikader & Bal 1981). Neoscona punctigera is a widespread species in Asia, with a range extending from Madagascar and surrounding islands to Japan, as well as south into New Guinea and northernmost Australia. Vernacular names for the species include ghost spider or monkey orb-weaver. Like many other orb-weavers, N. punctigera only puts up its web at night; it sits in the web head downwards. When morning comes, the spider consumes the previous night's web and finds a concealed spot to hide until evening. On the underside of the body, N. punctigera has one or two pairs of bright white spots. When the spider is hunkered down for the day, these spots are concealed but when the spider is out on its web at night they are very visible; Chuang et al. (2008) found that these bright spots appear to attract prey, as spiders who had had their spots painted over caught less moths than usual.

Male Neoscona punctigera, copyright Suresh Kumar.

The name 'monkey orb-weaver' refers to the appearance of the male, which like the males of other orb-weavers is quite a bit smaller than the female (I have no idea where the name 'ghost spider' comes from; perhaps something to do with the spider's appearance on a web?) Resting males tend to adopt a pose with the front legs bent close together and the rear legs crossed behind the abdomen (as in the photo just above). Combined with eye-like spots on the abdomen, the overall effect has been compared to a monkey lying back with its legs crossed and its hands behind its head.

Orb-weaver taxonomy can often be confusing. Early authors tended to dump a large number of orb-weavers in a broad genus Araneus; though this genus is now used in a much narrower sense, many orb-weaver genera are difficult to distinguish without examining the genitalia. Individual species can also be quite variable in superficial appearance with a lot of variation in colour pattern, so many species were initially described under a number of names. Female Neoscona differ from Araneus in the presence of a longitudinal groove on the cephalothorax, as well as the presence of one or two lateral lobes at the base of the scape (a projecting process over the epigyne, the sclerotised structure around the female genital openings). Distingushing N. punctigera from other species of Neoscona requires even closer inspection of the genitalia. In a number of older sources the species now generally referred to as Neoscona punctigera (including in the World Spider Catalog) is commonly referred to as 'Araneus lugubris'. Confusingly enough, the latter name actually has priority (it dates to 1841 whereas the name pectinigera was only published in 1857) but has fallen out of disuse since Grasshoff (1986) stated that it was preoccupied in a review of African Neoscona. I'm not sure if he was correct—I suspect that he thought it was antedated by Aranea lugubris, published in 1802 for what is now a species of wolf spider, but as the 1841 species was originally placed in the now-obsolete genus Epeira I don't think they actually conflict. Nevertheless, the rules governing how preoccupation affects the use of older names can be complicated and if N. pectinigera has been settled as standard then it may be best to let it be.

REFERENCES

Grasshoff, M. 1986. Die Radnetzspinnen-Gattung Neoscona in Afrika (Arachnida: Araneae). Annalen Zoologische Wetenschappen 250: 1–123.

Chuang, C-Y., E.-C. Yang & I.-M. Tso. 2008. Deceptive color signaling in the night: a nocturnal predator attracts prey with visual lures. Behavioral Ecology 19 (2): 237–244.

Tikader, B. K., & A. Bal. 1981. Studies on some orb-weaving spiders of the genera Neoscona Simon and Araneus Clerck of the family Araneidae (=Argiopidae) from India. Records of the Zoological Survey of India, Occasional Paper 24: 1–60.

The Velvet Spiders: High Society

Communal web of Stegodyphus, copyright V. B. Whitehead.

In John Wyndham's novel Web (published in 1979, some ten years after Wyndham's own death), a group of settlers attempting to establish a utopian society on a remote Pacific island find themselves besieged by spiders. Contrary to the usual solitary habits of their kind, the spiders of Web have evolved a social structure like that of wasps or ants, and form roving packs that can overwhelm and devour animals many times their size. Fortunately for us, no such rapacious beasts exist in real life. But there are social spiders, even if they do not present a threat to anything much larger than a big insect.

The social habit has evolved in spiders on a number of occasions, but is perhaps best developed in some species of the genus Stegodyphus. This is a genus of the family Eresidae, commonly known as the velvet spiders. Eresids are small spiders, distinguished from most others by their subrectangular carapace with the front edge produced into a hood above the chelicerae (Miller et al. 2012). They have the full spider complement of eight eyes, with the posterior median eyes generally enlarged and directed forwards. Together with their covering of plush fur (hence the name 'velvet' spiders), this gives them an appearance distinctly reminiscent of some sort of carnivorous muppet.

Male Eresus cinnaberinus, copyright Ferenc Samu.

There are nine currently recognised genera of eresids, though only Stegodyphus includes social species. The family is mostly restricted to the Old World, with a single species Stegodyphus manaus known from Amazonian Brazil. A second species, S. annulipes, was originally described as Brazilian, but has since been collected from Israel and appears to have been mislabelled (Miller et al. 2010). Members of the temperate Eurasian genus Eresus are commonly known as 'ladybird spiders' as males often have a striking abdominal colour pattern of black spots on a red background. Most eresids live in silken tubes under objects such as stones or underground, whereas Stegodyphus species construct their webs in vegetation (Miller et al. 2012).

Mature Stegodyphus lineatus feeding hatchlings, copyright jorgemotalmeida.

The communal webs of social Stegodyphus species may extend for several metres. When an animal becomes trapped in the web, as many spiders as are able to reach it swarm over, all biting and salivating as they can. As a result, the members of the colony are able to kill and digest much larger prey than they could otherwise handle alone. Sociality in Stegodyphus appears to have arisen as an extension of the parental care found in other eresids. Females of both Stegodyphus and Eresus will regurgitate food for newly hatched young (Kullmann 1972). In social Stegodyphus, young are cared for communally and females will feed the young of their nest-mates as well as their own. Eventually, the young begin feeding directly on the caring female herself, draining her haemolymph to the point of rapid death. Again, in social Stegodyphus, this fate awaits all mature adults in the colony, and there is no overlap between generations (Schneider 2002). After the death of their mother, juvenile Eresus and non-social Stegodyphus remain in a group until they are closer to maturity; social behaviour could have arisen through a simple delay in the time of dispersal.

REFERENCES

Kullmann, E. J. 1972. Evolution of social behavior in spiders (Araneae; Eresidae and Theridiidae). American Zoologist 12: 419–426.

Miller, J. A., A. Carmichael, M. J. Ramírez, J. C. Spagna, C. R. Haddad, M. Řezáč, J. Johannesen, J. Král, X.-P. Wang & C. E. Griswold. 2010. Phylogeny of entelegyne spiders: Affinities of the family Penestomidae (NEW RANK), generic phylogeny of Eresidae, and asymmetric rates of change in spinning organ evolution (Araneae, Araneoidea, Entelegynae). Molecular Phylogenetics and Evolution 55: 786–804.

Miller, J. A., C. E. Griswold, N. Scharff, M. Řezáč, T. Szűts & M. Marhabaie. 2012. The velvet spiders: an atlas of the Eresidae (Arachnida, Araneae). ZooKeys 195: 1–144.

Schneider, J. M. 2002. Reproductive state and care giving in Stegodyphus (Araneae: Eresidae) and the implications for the evolution of sociality. Animal Behaviour 63: 649–658.

The Running of the Spiders

Nursery-web spider Dolomedes minor, sitting atop its nursery web. Copyright Konstable.

Spiders are one of the most familiar groups of invertebrates out there. There's no denying this: everybody knows what a spider is. But for various reasons, the classification of spiders tended to lag a bit behind that of other terrestrial invertebrates. Being softer-bodied than insects, they tend not to exhibit the wealth of features that made many insect groups instantly discernible. To the modern arachnologist's eye, the earliest classifications of spiders can verge on the humorous. Latreille (1802), in his Histoire Naturelle des Crustacés et des Insectes, classified the entirety of what would now be called the araneomorph spiders into a single genus Aranea, divided into sections labelled not with formal names but with schematic diagrams of the arrangement of eyes found in that section.

A few decades later, in 1829 (translated into English in Cuvier, 1831), Latreille was to present a more detailed classification of the spiders, in which they were divided into groups largely on the basis of their life habits. The araneomorphs were hence divided between the Sedentariae, those spiders which captured their prey in webs or laid in ambush, and the Vagabundae, those spiders that actively hunted down their prey. The Vagabundae were in turn divided between two sections: the Citigradae or runners, and the Saltigradae or jumpers. Latreille's classification was subsequently more or less abandoned, as his behavioural groupings failed to line up directly with morphological clusters. Almost by accident, however, those taxa included by Latreille in his Citigradae have continued to be associated, and in modern classifications are classified within the Lycosoidea (Jocqué & Dippenaar-Schoeman 2007).

The lycosoids are, indeed, mostly active hunters. Their behaviour is reflected in the vernacular names of a number of the constituent families: the wolf spiders of the Lycosidae (previously featured here and here), the lynx spiders of the Oxyopidae, the prowling spiders of the Miturgidae. But the correspondence to Latreille's 'araignées loups' is not perfect: the Zoropsidae, for instance, are lycosoids that spin extensive webs. Nor are they mere rapacious hunters: many are devoted parents, carrying and/or guarding their egg-sacs to protect them from predators, and in the case of the Lycosidae even providing a certain degree of care for the newly hatched spiderlings.

One group of lycosoids has even gotten a name for parental care. The nursery-web spiders of the Pisauridae construct protective webs for their babies, containing them within a tent constructed by wrapping sheets of silk around suitable vegetation. When I was a child in New Zealand, I used to be fascinated by the nursery webs constructed by the species Dolomedes minor. Like many pisaurids, this species is associated with water, diving into it to hunt for fish and other small aquatic animals. The females would often build their nursery webs by tying together the ends of nearby rushes. Though it seems a little cruel to my adult self, the younger me loved to pull these webs apart to see the eruption of tiny spiders come scurrying out.

REFERENCES

Cuvier, G. 1831. The Animal Kingdom arranged in conformity with its organization, vol. 3. The Crustacea, Arachnides and Insecta, by P. A. Latreille, translated from the French with notes and additions, by H. M'Murtrie. G. & C. & H. Carvill: New York.

Jocqué, R., & A. S. Dippenaar-Schoeman. 2007. Spider Families of the World. Royal Museum for Central Africa: Tervuren (Belgium).

Latreille, P. A. 1802. Histoire Naturelle, générale et particulière des Crustacés et des Insectes, vol. 3. F. Dufart: Paris.

The Zealot Spiders

Female Zelotes longipes, photographed by Jørgen Lissner.

The spider in the photo above is a fairly typical representative of the genus Zelotes. As it currently stands, this is a large genus found worldwide, with around 400 species described so far and new ones continuing to debut at a fair rate of knots. I have no idea why Johannes Gistel, when he named this genus back in 1848, thought it to be especially zealous. My guess would be that there was probably no particular significance to the name; Gistel may have simply chose it in the well-established tradition of the time of providing organisms with classical names.

Members of the Gnaphosidae, the family of spiders to which Zelotes belongs, do not construct a permanent web but are ground-running active hunters. 'Running' being the operative word: part of the reason why new gnaphosid species continue to be described even from well-populated parts of the world is that, if you want to describe them, first you have to catch them. Zelotes species seem to be generalist in their habitats, with members of a single species found in a wide range of environments. Gnaphosids are something of a notoriously difficult group of spiders to identify, and Zelotes is no exception. Distinguishing features of Zelotes include the presence of a ventrodistal comb of stiff hairs on the metatarsi of the third and fourth pairs of legs, used in preening; the posterior median pair of eyes being roughly similar in size to the outer posterior eyes (gnaphosids have eight eyes in two rows of four); and the presence of an extra sclerite in the male genitalia (Ubick 2005). The genital sclerite was recognised as an important characteristic of the genus by Platnick & Shadab (1983), but their review was mostly restricted to North American species. Many species in other parts of the world remain unrevised, and future studies may affect their placement in Zelotes.

That said, most Zelotes species are fairly uniform in overall appearance (but then, so are gnaphosids in general). The species pictured at the top of this post is European. Compare it with a typical East Asian species:

Female Zelotes iriomotensis, photographed by Akio Tanikawa.

Or a North American species:

Female Zelotes fratris, photographed by Kyron Basu.

In general, the myriad Zelotes species can only be distinguished by examination of their genitalia. Most of us would be doing well to even identify it as a Zelotes.

REFERENCES

Platnick, N. I., & M. U. Shadab. 1983. A revision of the American spiders of the genus Zelotes (Araneae, Gnaphosidae). Bulletin of the American Museum of Natural History 174 (2): 97-192.

Ubick, D. 2005. Gnaphosidae. In: Ubick, D., P. Paquin, P. E. Cushing & V. Roth (eds) Spiders of North America: an identification manual, pp. 69-74. American Arachnological Society.

Lace Web Weavers

Male of the Madagascan Ambohima sublima, with enlarged inset of the clasping apparatus of metatarsus I, from Griswold et al. (2012).

The Phyxelididae, the lace web weavers, are one of the families of spiders to have appeared on the scene in recent years as a result of the collapse of the 'amaurobioids'. They are a family of smallish spiders found mostly in eastern Africa (including Madagascar). A single species, Phyxelida anatolica, is found in Cyprus and southeast Turkey, and the genus Vytfutia includes two species found in Sumatra and Borneo. Distinguishing features of the family include a series of thickened setae on the inner side of the pedipalp femur in both sexes. These are expected to function as a stridulatory apparatus; this has not yet been robustly confirmed, though individuals have been observed making jerking movements of the palp prior to copulation that may suggest stridulation (Griswold et al. 2012). Another significant feature is the presence in most species of modified first (and sometimes second) metatarsi in the males, used for grasping the female during mating (Griswold et al. 2012). In Vytfutia and members of the tribe Phyxelidini, a large articulate spur atop an apophysis on the metatarsus sits against a spinose depression. In the tribe Videoleini, there is no spur but there may still be a spinose apophysis (Griswold 1990).

Web of Ambohima sublima photographed by Joel Ledford, from Griswold et al. (2012).

Phyxelididae produce tangled or sheet webs from cribellate silk, which they generally place in secluded locations such as under rocks or logs (a few tropical African species are found in caves). For the most part, the family exhibits what is known as an 'afromontane' distribution: though found in most altitudes in the southernmost part of Africa, tropical African members of the family are restricted to alpine localities or caves. The southeast Asian Vytfutia, placed by Griswold (1990) as the sister taxon to the other phyxelidids, differs in being found in a lower altitude in primary rainforest. A molecular analysis by Griswold et al. (2012) agreed with the morphological analysis of Griswold (1990) in separating Vytfutia from the rest of the Phyxelididae (the molecular analysis also failed to confirm monophyly of Phyxelididae including Vytfutia, but its coverage was perhaps not adequate to make this a reliable result). However, rather than dividing the African phyxelidids between the Vidoleini and Phyxelidini, Griswold et al.'s (2012) analysis placed the Vidoleini as a monophyletic subgroup of a paraphyletic Phyxelidini. Nevertheless, this would strengthen Griswold's (1990) earlier inference that the modified metatarsus I was part of the ancestral morphology of the Phyxelididae, and its absence in certain Vidoleini a secondary loss.

South African phyxelidid photographed by Alan. Though identified as a possible Vidole species, the morphology of metatarsi I indicates a member of the Phyxelidini.

REFERENCES

Griswold, C. E. 1990. A revision and phylogenetic analysis of the spider subfamily Phyxelidinae (Araneae, Amaurobiidae). Bulletin of the American Museum of Natural History 196: 1-206.

Griswold, C. E., H. M. Wood & A. D. Carmichael. 2012. The lace web spiders (Araneae, Phyxelididae) of Madagascar: phylogeny, biogeography and taxonomy. Zoological Journal of the Linnean Society 164: 728-810.

More Wolfies (Taxon of the Week: Artoriinae)

Artoria mckayi, an inhabitant of alpine gravel river banks in eastern Australia. Photo by D. Paul.

Wolf spiders, or "wolfies" as I tend to refer to them, were previously covered here in an earlier post. The subject of today's post is one of the specific subgroups of wolf spiders, the Artoriinae.

Though one of primary assemblages of wolf spiders in the Australian region, the Artoriinae were only formally established as a distinct group in 2007 (Framenau, 2007). The group had previously been identified in molecular phylogenies as an unnamed clade sister to the combined clade of the subfamilies Lycosinae and Pardosinae. At least one morphological character has also been identified supporting the clade, the presence of a basal apophysis (side-branch) on the embolus, the intromittent part of the male's copulatory pedipalp.


A Tetralycosa specimen captured in the Great Victoria Desert. Photo by June Hudson.

Artoriinae are primarily restricted to Australia and the Pacific islands except for Artoria parvula which is found from northern Australia to the Philippines. Inclusion of the Sumatran Lycosella tenera is contingent on whether or not it is truly congeneric with Hawaiian Lycosella species (Framenau, 2007) while three African species listed in Artoria by Platnick's World Spider Catalog owe their position to Carl-Friedrich Roewer, whose classification of wolf spiders is generally regarded as unmitigated bollocks, and require a second look. More recently, it was suggested that the South American genera Lobizon and Navira may warrant consideration as possible artoriines (Piacentini & Grismado, 2009). Framenau (2007) placed eight genera in the Artoriinae (including Lycosella) plus two probable undescribed genera; Framenau's (2007) "new genus 2" has since been dubbed Kangarosa* (Framenau, 2010).

*One of the new Kangarosa species was named by Volker Framenau after his recently born son, placing Yannick Framenau in an exclusive club of people to have a new species named after them before they've even completed toilet training.


Lobizon corondaensis, an Argentinian species that may or may not be related to the Artoriinae. From Piacentini & Grismado (2009). 'Lobizón' is apparently Spanish for 'werewolf'.

Like other wolf spiders, artoriines are mostly conservative in their overall appearance. They do exhibit a reasonable size range, from the 2.6 mm Artoria palustris to 25 mm Tetralycosa species. Males of the South-West Australian species Artoria schizocoides possess a unique brush of spatulate setae on the underside of the first tibia (Framenau & Hebets, 2007). The members of the genus Tetralycosa are burrowing species that are invariably found in high salinity environments such as around salt lakes.

REFERENCES

Framenau, V. W. 2007. Revision of the new Australian genus Artoriopsis in a new subfamily of wolf spiders, Artoriinae (Araneae: Lycosidae). Zootaxa 1391: 1-34.

Framenau, V. W. 2010. Revision of the new Australian wolf spider genus Kangarosa (Araneae: Lycosidae: Artoriinae). Arthropod Systematics and Phylogeny 68 (1): 113-142.

Framenau, V. W., & E. A. Hebets. 2007. A review of leg ornamentation in male wolf spiders, with the description of a new species from Australia, Artoria schizocoides (Araneae, Lycosidae). Journal of Arachnology 35 (1): 89-101.

Piacentini, L. N., & C. J. Grismado. 2009. Lobizon and Navira, two new genera of wolf spiders from Argentina (Araneae: Lycosidae). Zootaxa 2195: 1-33.

Big Bad Wolfies (Taxon of the Week: Lycosidae)

Female wolf spider with an abdomen-load of young. Photo by J. Centavo.

The wolf spiders (I usually call them simply 'wolfies') of the family Lycosidae are one of the more easily recognisable groups of ground-dwelling spiders. Their eyes are placed in three rows clustered together at the front of the cephalothorax with the median posterior eyes large and sitting above a straight row of the small anterior eyes. Some wolf spiders reach relatively large sizes and large wolfies tend to usually be some variant of brown or grey with longitudinal stripes. Most members of the family, particularly the larger species, tend to be morphologically quite conservative and despite the recognition of well over 2000 species in the family (a number that is increasing with no sign of slowing down) distinguishing those species is not usually easy without close examination. Wolf spiders are not often inclined to bite humans and their bites are not usually regarded as dangerous (though a bite from a large species could be painful).


A slightly more distinctively coloured member of the family - Geolycosa archboldi from central Florida. Photo by H. K. Wallace.

Wolf spiders get their name because most members of the family are active hunters rather than snare builders though a smaller number of genera build distinctive sheet webs with a silk retreat tunnel. Most authors have regarded the sheet web builders as retaining the ancestral behaviour for the family but phylogenetic analysis has not determined this conclusively (Murphy et al., 2006); if web building is ancestral then it has been convergently lost on numerous occasions. Those lycosids that do not build sheet webs may be permanently vagrant or they may dig themselves a home burrow into which they retreat when not hunting. All wolf spiders wrap their eggs in a silken egg-sac which the female carries on the underside of her spinnerets; after the eggs hatch she carries her young around clinging to her abdomen.


A more typical lycosid photographed by Sander van der Molen.

Recent studies have shown the need for a fair amount of revision of lycosid systematics; the main genus Lycosa in particular had been shown to be a polyphyletic assemblage of conservative large lycosids. Researchers are slowly chipping away at the necessary revisions; a great deal of progress has been made (see, for instance, Volker Framenau's webpage on Australian lycosids), but a great deal remains to be done. Matters have not been helped by the fact that wolf spiders were another group of arachnids to be subjected to the loving care and attention of Carl-Friedrich Roewer, demonstrating his usual talent for producing extensive revisions based on the most superficial and inconsequential of characters. Also, until recently there was debate over the identity of Lycosa's type species, the Mediterranean L. tarantula originally named by Linnaeus. This species, it should be noted, was the original tarantula; it was only later that the name became associated with South American mygalomorph spiders.

REFERENCES

Murphy, N. P., V. W. Framenau, S. C. Donnellan, M. S. Harvey, Y.-C. Park & A. D. Austin. 2006. Phylogenetic reconstruction of the wolf spiders (Araneae: Lycosidae) using sequences from the 12S rRNA, 28S rRNA, and NADH1 genes: implications for classification, biogeography, and the evolution of web building behavior. Molecular Phylogenetics and Evolution 38 (3): 583-602.

Taxon of the Week: Amphinectidae

Male of Metaltella simoni, a South American spider that has become established in the southern United States. Photo by johnnyn.

The Amphinectidae are a family of spiders described from Australia, New Zealand and South America. They are members of the 'amaurobioid' group of spiders, and share all the issues of poor definition associated with that group. Indeed, Davies (2002) made the admission that "there is no clear diagnosis of the family Amphinectidae". In general, most amphinectids are ground-dwelling (like many other 'amaurobioids'), and they are active hunters or construct small sheet-webs. They have two nearly straight rows of four eyes each at the very front of the cephalothorax. The metatarsi of the thrid and fourth legs have preening combs (Griswold et al., 2005). Since the Amphinectidae was originally established for a group of sixteen New Zealand genera, it has been enlarged to include the Australian and South American subfamily Metaltellinae (Davies, 1998) and the Tasmanian Tasmarubriinae (Davies, 2002). A further subfamily, the Kababininae, was initially regarded as amphinectid but has since been removed (Davies, 1999). Oddly enough, while the use of the names "Metaltellinae" and "Tasmarubriinae" would seem to imply an "Amphinectinae" (probably for the original New Zealand genera), I haven't been able to find a single case of such a name being used. Norm Platnick's World Spider Catalog simply lists the genera in this family in alphabetical order, without using subdivisions.

Metaltellinae are a reasonably distinct group - they differ from all other 'amaurobioids' in that the embolus (the intromittent part of the male genitalia through which the end of the sperm duct passes) turns anticlockwise rather than clockwise as in other families (Davies, 1998). Of the ten genera included in this subfamily by Davies (1998), eight are Australian and two (Metaltella and Calacadia) are South American, but I would not be surprised if this difference simply reflects the better-studied nature of Australian spiders. A single South American species, Metaltella simoni, has been introduced to southern North America with records from Florida to California. A relationship between Amphinectidae and Metaltellinae was first supported by Griswold et al. (1999), with the supporting characters being a proximal dorsal process on the tibia of the male pedipalp and possession by the females of a convoluted vulva*. The subfamily Tasmarubriinae was established by Davies (2002) and distinguished from Amphinecta (but not necessarily the other amphinectid genera, which were not examined) on the basis of features of the male genitalia.

*Davies (1998) had already transferred the Metaltellinae into the Amphinectidae on the basis that her own phylogenetic analysis "showed" the Metaltellinae to be closer to the Amphinectidae than to the Amaurobiidae (among which they had previously been included). However, Davies' analysis only included representatives of Amaurobiidae, Amphinectidae and Metaltellinae, with the single amaurobiid set as the outgroup, so it would have been impossible for the analysis to have shown anything else.


Unidentified amphinectid from Southland, New Zealand. Photo from here.

Other analyses have not supported an exclusive Amphinectidae-Metaltellinae connection. Davies (1999) included representatives of New Zealand Amphinectidae, Tasmarubriinae and Metaltellinae in an analysis of 'amaurobioid' spiders; while Tasmarubriinae and Amphinectidae formed a clade (supported by the first leg in females being shorter than the fourth leg, the presence of metatarsal preening combs, and a rounded conductor as part of the male genitalia), Metaltellinae were not part of that clade. Griswold et al. (2005) placed their included representatives of the two as successive outgroups to a clade of Desidae (marine spiders) and Dictynidae (slater spiders)*. Griswold et al. (1999) recognised a "fused paracribellar clade" including Amphinectidae, Desidae, Agelenidae, Stiphidiidae and Neolana, supported by features of the silk-spinning organs. This clade was still recognised by Griswold et al. (2005) but with slightly different contents, including the Dictynidae and excluding the Stiphidiidae.

*It is also noteworthy that neither of the two analyses by Griswold et al. (1999, 2005) have supported a close connection between Amphinectidae and Neolana, a genus included in Amphinectidae by Platnick's Spider Catalog, but placed in its own family by many other authors.

One final thing, which has nothing to do with the previous paragraphs, but which I felt compelled to include. The following passage is taken from a description of a New Zealand genus of Amphinectidae in Forster & Forster (1999):

Although the Otago species, Akatorea otagoensis, was occassionally found in rotting logs like its Fiordland relative, it was surprisingly rare until a sudden emergency with drains on our Dunedin property required an excavation. A metre or so below the surface of our lawn the likely answer to the true home of these spiders was revealed. There, lining the cracks and crevices in the clay subsoil, were webs (and eggsacs) all inhabited by these pale straw-coloured spiders, which proved to be the previously rare Akatorea otagoensis.

Science is often a matter of detailed planning and careful investigation. However, never underestimate the importance on many an occassion of sheer dumb luck.

REFERENCES

Davies, V. T. 1998. A revision of the Australian metaltellines (Araneae : Amaurobioidea : Amphinectidae : Metaltellinae). Invertebrate Taxonomy 12: 211-243.

Davies, V. T. 1999. Carbinea, a new spider genus from north Queensland, Australia (Araneae, Amaurobioidea, Kababininae). Journal of Arachnology 27 (1): 25-36.

Davies, V. T. 2002. Tasmabrochus, a new spider genus from Tasmania, Australia (Araneae, Amphinectidae, Tasmarubriinae). Journal of Arachnology 30 (2): 219-226.

Forster, R. R., & L. M. Forster. 1999. Spiders of New Zealand and their Worldwide Kin. University of Otago Press: Dunedin (New Zealand), and Otago Museum: Dunedin.

Griswold, C. E., J. A. Coddington, N. I. Platnick & R. R. Forster. 1999. Towards a phylogeny of entelegyne spiders (Araneae, Araneomorphae, Entelegynae). Journal of Arachnology 27: 53-63.

Griswold, C. E., M. J. Ramírez, J. A. Coddington & N. I. Platnick. 2005. Atlas of phylogenetic data for entelegyne spiders (Araneae: Araneomorphae: Entelegynae) with comments on their phylogeny. Proceedings of the California Academy of Sciences, Fourth Series 56 (suppl. 2): 1-324.

Attercop

Permarachne novokshonovi, a Permian fossil that was similar in appearance to the Devonian Attercopus fimbriunguis. Figure from Selden et al. (2008).

Selden, P. A., W. A. Shear & M. D. Sutton. 2008. Fossil evidence for the origin of spider spinnerets, and a proposed arachnid order. Proceedings of the National Academy of Sciences of the USA 105 (52): 20781-20785.

A new paper published today presents us with a revised description of Attercopus fimbriunguis, the stem-spider (thanks to William Shear, one of the paper's authors, for sending it out). With this redescription, the position of Attercopus is secured as one of palaeontology's great "transitional fossils".

Attercopus is a fossil arachnid from the Middle Devonian (bonus question: what is the connection between Attercopus and Barad-dur?), so dates back to when the terrestrial environment was first finding its feet (and in those invertebrate-dominated days, there were often a lot of them to find). Most modern terrestrial animals were yet to make an appearance - the vertebrates were still keeping to the water, the insects were there but not yet a significant part of the ecosystem. It was the age of the arachnids and myriapods. Even within the arachnids, most of the taxa then present would have been unfamiliar to modern humans, and the currently most familiar group of arachnids, the spiders, had not yet made an appearance. That is where Attercopus becomes so significant.

Spiders are actually not typical arachnids at all. Like all other arthropods, the ancestral arachnid form has the body divided up into segments. These segments are externally visible as the cuticle is divided into plates, with separate dorsal (tergites) and ventral (sternites) plates. In most living arachnid orders (such as scorpions and harvestmen), these external plates are still present. In most spiders, the cuticular plates have become fused, and the segmentation is not externally visible. One small group of spiders that is today restricted to eastern Asia, the Mesothelae or liphistiomorphs, differ from all other living spiders (the Opisthothelae, to which they form the sister group) in retaining visible tergites on the opisthosoma (abdomen), though they do not have visible sternites. Mesothelae also differ from Opisthothelae in lacking poison glands in the fangs. As well as the concealed segmentation (independently acquired by acaromorphs such as mites), spiders are also distinct in their production of silk. Only one other group of arachnids, the pseudoscorpions (as well as numerous groups of insects), produces silk. In pseudoscorpions, the silk-producing glands are in the pedipalps. In spiders, they are at the back end of the underside of the opisthosoma, and open through appendages called spinnerets (photo below from here).



The presence of silk-producing spigots in Attercopus was first established in 1991, when it was connected to an isolated Devonian 'spinneret' described two years previously (Selden et al., 1991). As redescribed by Selden et al. (2008), however, Attercopus shows a number of significant differences from modern spiders. It retains distinct external segmentation, both tergites and sternites. Also, rather than having the silk glands on spinnerets, the spigots are positioned directly on the underside of the opisthosoma (and their status as silk glands is confirmed in one specimen by the presence of a strand of silk preserved in the process of being exuded from one of the spigots!) The 'spinneret' previously described for Attercopus, as it turns out, was an artifact resulting from post mortem folding of the cuticle. Without the guiding control of spinnerets, Attercopus would not have produced silk in well-defined strands like a modern spider, but in more of a shapeless mat. This is not surprising - the distribution of silk use in modern spiders suggests that its use in reproductive functions (constructing egg cases, spermatophores, etc.) or in constructing burrows probably pre-dated its use in prey capture.


Part of a fossilised Attercopus, showing silk preserved while being released from one of the spigots. Figure from Selden et al. (2008).

Attercopus also appears to have lacked poison glands (again, their previously-suggested presence appears to have been an artifact), which tallies well with their absence in living Mesothelae. Perhaps most intriguing of all (at least to me) is that Attercopus possessed a segmented flagellum. The flagellum is a character of the Uropygi (whip scorpions) which, together with the Amblypygi, form the probable living sister group to spiders in the clade Tetrapulmonata (Shultz, 2007). At present, we cannot say whether the flagellum is an ancestral feature of Tetrapulmonata that was lost in spiders and amblypygids, or was independently derived in uropygids and Attercopus. Selden et al. (2008) also identify sternites and a flagellum in a Permian spider-like fossil, Permarachne novokshonovi, and establish a new order, Uraraneida, for the two fossils. This is not a major change in classification, as Uraraneida is still regarded as the stem group to modern spiders. Also, as the characters uniting Attercopus and Permarachne (free sternites and a flagellum) are both probably plesiomorphies, the Uraraneida is not necessarily monophyletic. With the definite exclusion of Attercopus from the crown group, the earliest known true spider is now Palaeothele montceauensis, a liphistiomorph from the late Carboniferous.


Liphistius owadai, a modern species of spider retaining free tergites. Photo from here.

The big change between Attercopus and crown Araneae seems to have been the development of spinnerets instead of bare spigots. Developmental genetic studies show that the spinnerets are homologous to opisthosomal legs, which is remarkable because arachnids don't have legs on the opisthosoma. To find opisthosomal appendages on the arachnid lineage, one has to go to their living sister group, the horseshoe crabs. Because of the derived position of spiders within arachnids, and the fact that all other fossil arachnids lack opisthosomal appendages, it is unlikely that opisthosomal appendages in spiders represent a retained plesiomorphy that was lost in all other arachnids. Selden et al. (2008) suggest that this may represent reactivation of suppressed developmental genes, as supposedly seen in stick insects. But despite my wince at their ill-chosen supporting example, legs-to-spinnerets is perhaps a good candidate for such a process. While obvious opisthosomal appendages are not present in arachnids, developmental studies indicate that the covering plates of the arachnid book lungs are homologous to appendages, and it has been suggested for scorpions that the sternites themselves represent fused appendage remnants.

The sad fact, I feel, is that our understanding of how developmental processes evolve is still all too rudimentary. For all the vast amount of genetic studies that have been conducted in recent decades, most have been focused on a relatively small number of model species - Drosophila melanogaster, Danio rerio, Arabidopsis thaliana,... Consideration of a single species, or even a few closely-related species as has been done for Drosophila, becomes woefully inadequate when considering questions raised when debating the possibility of genetic recurrence. What happens to a developmental gene when it is inactivated for a certain function? Can it be readily reactivated, or does genetic drift seal its fate as a pseudogene? Is genetic reactivation even the only possible explanation - what about those genes that are still developmentally functional elsewhere in the body? Can they become activated elsewhere in the embryo to give rise to novel structures? Could the spinnerets of spiders be not recurrences of the lost opisthosomal appendages, but rather re-deployments of the appendages still present on the prosoma? Or could they somehow represent a combination of the two? Whatever the answers that are yet to be found, fossils such as Attercopus will always be critical in directing our searches for them.

REFERENCES

Selden, P. A., W. A. Shear & P. M. Bonamo. 1991. A spider and other arachnids from the Devonian of New York, and reinterpretations of Devonian Araneae. Palaeontology 34: 241–281.

Shultz, J. W. 2007. A phylogenetic analysis of the arachnid orders based on morphological characters. Zoological Journal of the Linnean Society 150 (2): 221-265.

Salticid Spider Bollocks

The "information sheet" below was forwarded to my e-mail this afternoon. The person who forwarded it to me did so as a joke, but apparently it has taken some people in:

Really terrifying

Three women turned up at hospitals over a 5-day period, all with the same symptoms.
Fever, chills, and vomiting, followed by muscular collapse, paralysis and finally, death..

There were no outward signs of trauma.

Autopsy results showed toxicity in the blood. These women did not know each other and seemed to have nothing in common. It was discovered, however, that they had all visited the same Restaurant (Olive Garden , Western Cape ) within days of their deaths. The Health Department descended on the restaurant , shutting it down. The food, water, and air conditioning were all inspected and tested, to no avail.
The big break came when a waitress at the restaurant was rushed to the hospital with similar symptoms. She told doctors that she had been on vacation, and had only went to the restaurant to pick up her check.

She did not eat or drink while she was there, but had used the restroom
That is when one toxicologist, remembering an article he had read, drove out to the restaurant, went into the restroom and lifted the toilet seat

Under the seat, out of normal view, was a small spider. The spider was captured and brought back to the lab, where it was determined to be the Two-Striped Telamonia (Telamonia dimidiata), so named because of its reddened flesh color. This spider's venom is extremely toxic, but can take several days to take effect. They live in cold, dark, damp climates, and toilet rims provide just the right atmosphere..

Several days later a lawyer from Jacksonville showed up at a hospital emergency room. Before his death, he told the doctor, that he had been away on business, had taken a flight from Indonesia , changing planes in Singapore , before returning home He did NOT visit (Olive Garden), while there. He did (as did all of the other victims) have what was determined to be a puncture wound, on his right buttock. Investigators discovered that the flight he was on had originated in India .
The Civilian Aeronautics Board (CAB) ordered an immediate inspection of the toilets of all flights from India and discovered the Two-Striped Telamonia (Telamonia dimidiata) spider's nests on 4 different planes!
It is now believed that these spiders can be anywhere in the country.
So please, before you use a public toilet, lift the seat to check for spiders. It can save your life!




And please pass this on to everyone you care about.

Aww, look! It's a salticid! Innit cute?

I find it fitting that I am writing this post in Australia - which, as we all know, is the spiritual home of all toilet-seat lurking spiders. Not surprisingly, this particular story is total bollocks. And according to Snopes, it's ancient bollocks - this story has been floating about the interweb since 1992, albeit with the occasional variation to where exactly it's supposed to have taken place. Snopes also notes that the "Civil Aviation Board" referred to garbledly in the e-mail hasn't been in existence since 1984. I noticed the problem with "They live in cold, dark, damp climates, and toilet rims provide just the right atmosphere.." Ummm, a toilet-seat isn't a damp climate at all - quite the opposite - and any spider wanting to occupy the damp space under the rim is going to want to have invested in some scuba gear any time anyone flushes.

I'll put this simply ('scuse caps) - THERE ARE VERY FEW SPIDERS THAT CAN HARM YOU. Of those spiders that can harm you (and Telamonia dimidiata - scroll down a bit if you click the link - ain't one of them), even fewer of them are likely to come into contact with you. "Toxic" is not necessarily the same as "dangerous" - most toxic animals such as venomous snakes and spiders are far more likely to discretely get out of your way rather than attack. You probably won't even know they were there.

The Strangest of Spiders

In the comments to an earlier post, I promised to write a post sometime on micro-spiders. As alluded to in that post, some of the smallest spiders are mind-bogglingly tiny - the smallest known male spider, Patu digua, reaches all of 0.37 mm in length as an adult, but at least one other species known as yet only from females could potentially have a male even smaller. If one of these spiders crawled into your ear while you were sleeping, it could probably slip into your Eustachian tubes and tap on the back of your eyeballs. But even more remarkable than their small size is the bizarre morphologies on show among the micro-spiders. And no group of micro-spiders is more bizarre than the Archaeidae.

Archaeids are a bit bigger than Patu, but still pretty small - the largest examples reach about six millimetres. The name "Archaeidae", of course, means "old", and archaeids received their name because they were first described in 1854 from fossils in Baltic amber from northern Europe. In Europe, the archaeids are long gone (they may have disappeared along with the amber forests), but nearly thirty years after their initial description living examples were found in Madagascar. They are also known from Australia, while a specimen from Cretaceous Burmese amber has been placed in a living genus from South Africa and Madagascar (Penney, 2003). A species has also been described from the Jurassic of Kazakhstan, but it is uncertain whether this species is an actual archaeid or belongs to another micro-spider family such as Pararchaeidae.

Many micro-spiders show relatively long chelicerae (the fangs and their base) relative to body size, but in Archaeidae this is taken to the extreme, as can well be seen in the photo by Jeremy Miller at the top of this post. Because the trochanter (base) of the chelicerae is a rigid structure, lengthening them in spiders requires that the carapace as a whole be raised, otherwise the fangs would not be able to get anywhere near the mouth. Archaeids have developed a long "neck" supporting the eyes and chelicerae. The distinct shape of the cephalothorax together with the long chelicerae gives them an unmistakeable profile, and one common name used for the group is "pelican spiders". Despite their small size, archaeids are active hunters and voracious exclusive predators of other spiders (another common name is "assassin spiders"). It has been suggested that the lengthened chelicerae are directly related to their araneophagous diet, allowing them to strike their prey without getting too close, but as I already noted archaeids are not the only small spiders with lengthened chelicerae (though they are still the most dramatic), and I'd be interested to know if there is a correlation between small size and long chelicerae.



I'd also like to share this diagram from Wood et al. (2007) showing a molecular-derived phylogeny of the endemic Madagascan genus Eriauchenius. As can be seen, there is a fair amount of variation in the thickness of the "neck" (the darkness of the bars reflects the mean carapace height/length ratio for whichever group they subtend), and it had been suggested that those species with a particularly slender neck formed a derived clade. Wood et al. (2007) found that this does not appear to be the case, with at least two extreme narrow-neck groups - E. workmani in one and E. gracilicollis and E. lavatenda in the other - at quite divergent points in the tree. I also looks to me like at least one group - E. tsingyensis and its allies - may have gone the other way. To paraphrase a Rocky Horror Picture Show audience member - that spider has no neck.

REFERENCES

Penney, D. 2003. Afrarchaea grimaldii, a new species of Archaeidae (Araneae) in Cretaceous Burmese amber. Journal of Arachnology 31 (1): 122-130.

Wood, H. M., C. E. Griswold & G. S. Spicer. 2007. Phylogenetic relationships within an endemic group of Malagasy ‘assassin spiders’ (Araneae, Archaeidae): ancestral character reconstruction, convergent evolution and biogeography. Molecular Phylogenetics and Evolution 45 (2): 612-619.

Amaurobioidea: Rummaging through a Wastebasket

A representative of the strikingly-coloured Nicodamidae from Australia. Photo by Nick Monaghan. While such spiders were previously identified as Nicodamus bicolor, there are no less than 23 species in seven genera that have previously been included under that name.

One term that you may come across in discussions of phylogeny is the concept of a "wastebasket" taxon. As the name suggests, a wastebasket taxon is one into which authors tend to throw everything that they can't really deal with. Often, a wastebasket will include the members of a group that are relatively unspecialised, often primitive, and united less by their shared characters than their lack of distinct features to connect them to one or another of the specialised subgroups that the author may recognise within the parent group. Phalangodidae among short-legged harvestmen, Sylviidae among passerine birds and Perciformes among spiny-finned fishes are all examples of taxa that have become wastebaskets in the past. Some wastebasket taxa are explicitly established as such, like the 'Deuteromycota' that included asexual fungi before techniques were developed that made it significantly easier to relate asexual and sexual fungal taxa. More often, though, a taxon originally based on a certain combination of features will develop into a wastebasket over time as phylogenetic studies show that the original basis characters for that taxon represent plesiomorphies (ancestral characters). This week's highlight taxon, the spider superfamily Amaurobioidea, perhaps belongs to the latter group.


Tegenaria gigantea (Agelenidae). Photo from Wikipedia. Agelenids build funnel-shaped webs and are apparently often called some variant of "funnel spiders" in North America, but such names are likely to cause confusion here in Australia with a certain notorious mygalomorphs. Some species of Tegenaria such as the hobo spider are also known for being toxic, but nowhere near as toxic as the Australian funnel-web.

In an earlier post, I included a quick overview of basal spider phylogeny, going as far down as the clade Araneoclada that unites those spiders that have only a single pair of book lungs (ancestrally, at least - many families of Araneoclada have lost the book lungs entirely, or evolved tracheae in their place). Members of the Araneoclada are further divided between the Haplogynae and the Entelegynae, originally based on the presence (Entelegynae) or absence (Haplogynae) in females of paired copulatory ducts opening on a sclerotised plate called the epigyne. While the absence of such ducts in the Haplogynae is obviously a primitive character and no longer regarded as uniting them, the group has funnily enough been supported as monophyletic based on a number of other characters (except for a small number of 'haplogyne' taxa that are phylogenetically entelegynes) (Coddington & Levi, 1991). However, the Amaurobioidea belong to the Entelegynae, which is by far the larger of the two clades. Within the Entelegynae, the primary division was long based on whether or not a species possessed a cribellum, a plate-like structure among the spinnerets that bears hundreds of tiny silk-producing spigots. As these spigots exude silk simultaneously, the spider uses a specialised arrangement of bristles on the fourth pair of legs to weave them together to form a woolly thread (see here for a more detailed description). Because this woolly thread is composed of multiple tangled strands, it can effectively entangle prey such as small insects that get caught among the strands. Unfortunately, as knowledge of entelegyne spiders improved it became clear that possession of a cribellum did not define a phylogenetically coherent group. A number of cases were identified of pairs of taxa clearly related by other characters in which one taxon possessed a cribellum and the other did not. The eventual conclusion was that the cribellum was an ancestral character for the Entelegynae (as also supported by its presence in one haplogyne family, the Filistatidae) that had been lost on numerous occassions.


Ctenus floweri (Ctenidae), from Singapore. Photo by David Court. Ctenids are active hunters.

In general, the Amaurobioidea included cribellate spiders with unbranched abdominal median tracheae, as opposed to Dictynoidea with branched abdominal median tracheae (Coddington & Levi, 1991). Families that have been assigned to Amaurobioidea include (among others) Amaurobiidae, Agelenidae, Ctenidae, Amphinectidae and Nicodamidae, but relatively little unites these families. Most of them are generally ground-dwellers (which may explain the common name of one of the best-known members, the hobo spider Tegenaria agrestis). Many members build small sheet-webs, but others are active hunters. Both the characters referred to above have since been shown to represent plesiomorphies of larger clades, with the alternative conditions arising multiple times. The phylogenetic analysis of entelegyne spiders by Griswold et al. (1999) found the 'Amaurobioidea' to fall within a clade that was sister to the clade including the orb-weavers, but the same clade included the Dictynoidea and Lycosoidea (wolf spiders and such) nested within 'amaurobioids'. Indeed, not even the type family of Amaurobiidae was monophyletic, with some members closer to the lycosoids while others were closer to the agelenoids. The Amaurobioidea, it seems, was a bust.

Coming up - science and art, whether taxonomy is science, why family names are so awful, micro-spiders, and Parapseudoleptomesochrella almoravidensis.

REFERENCES

Coddington, J. A., & H. W. Levi. 1991. Systematics and evolution of spiders (Araneae). Annual Review of Ecology and Systematics 22: 565-592.

Griswold, C. E., J. A. Coddington, N. I. Platnick & R. R. Forster. 1999. Towards a phylogeny of entelegyne spiders (Araneae, Araneomorphae, Entelegynae). Journal of Arachnology 27: 53-63.

Araneidae - With Web and With Scent

The St. Andrew's Cross (Argiope keyserlingi). Photo by Louise Docker.

The orb-weavers are undoubtedly the best-known of all spiders. Ask anyone to imagine a spider and they will probably picture an orb-weaver (they may also have transcribed the words "some pig" in the web). This is something of an unfair characterisation - of the more than 100 recognised families of spiders, less than ten are orb-weavers. Still, it is one of the orb-weaving genera that holds the name of "spider", Araneus, which, as the only generic name used in Clerck's (1757) Aranei Svecici, the only taxonomic work recognised by the ICZN that predates the 1758 tenth edition of Linnaeus' Systema Naturae, is officially the oldest generic name in zoological nomenclature*. That's right - spiders came before humans. Nyeh nyeh nyeh.

*Admittedly Clerck did use the name Araneus for all spiders, not just species included in the modern Araneus.

The Araneidae are the largest family of orb-weaving spiders, with a little less than 3000 described species. They are actually a lot more numerous than you might realise - many species build their webs only at night, taking them down in the morning before hiding during the day and rebuilding the web every evening. The family is decidedly diverse in appearance - from the gaudy colours and spines of the Christmas spiders to the idiosyncratic figures of the tailed spiders to one group whose common name describes their appearance perfectly - the bird-dropping spiders.



The classic orb-web is made by first floating a line of sticky silk horizontally across a space between two anhoring points (such as a pair of branches), then running a second looser non-sticky strand along the initial strand. The spider then drops herself* from the centre-point of the second strand, trailing a third strand behind her, so that the second and third strands form a Y-shape. The vertex of the Y will be the centre of the web. The spider next constructs an outer frame, as shown above in a diagram by Ed Nieuwenhuys (the page linked to has diagrams of each of the stages in orb-web construction), then runs a series of spokes from the centre of the web to the outside. She then runs a broad spiral of non-sticky thread from the centre of the web until she reaches the outer edge. After that, it travels back to the centre laying a much tighter spiral of sticky thread, removing the non-sticky scaffold as she goes. As the sticky thread is stretched, the sticky coating breaks into a series of globules of coiled thread, which is how the web is able to be so elastic and stand up to the thrashings of captured prey. The spider herself is able to move about without being trapped by means of secretions produced by glands near the mouth with which she coats her legs. Forster & Forster (1999) refer to an experiment where the tips of a spider's legs were dipped in solvent before the spider was returned to its web. The spider initially showed great difficulty in moving due to the removal of its protective coating, though it was able to renew the covering and regain mobility. After the web has been completed, the spider will take up residence at the central hub, legs resting on the radiating spokes in order to feel for any vibrations. Araneid eyesight is almost non-existent, and orb-weavers are incapable of hunting without a web. They are perhaps the closest thing to a terrestrial filter-feeder, filtering the air for small animals.

*All spiders are referred to as female unless proven otherwise, like ships and birds of prey. It's another one of those things that make the English language so damn confusing.


An unidentified member of the genus Gasteracantha. These spiders come in a dazzling array of colours and ornamentations, and unlike many other araneids are often visible during the day, earning them such names as "jewel spider" or "Christmas spider". Colour patterns can vary significantly even between members of the same species. Photo from here.

Many araneids may vary the basic orb-web design further. Ladder-web spiders, for instance, have a long narrow web instead of the usual circle. The function of these is not really understood, though it has been suggested as a specialisation for catching moths - moths have a covering of loose scales on their wings which would normally allow them to shake off a web and escape, but it is suggested that the elongate shape of a ladder-web means that as the moth shakes off its scales, it falls onto a lower part of the web until eventually it is no longer able to escape. Many orb-weavers construct a stabilimentum, a zig-zag ladder-shaped structure that extends upwards from the central hub. Again, despite being such a distinctive structure, the function of the stabilimentum remains largely unknown, though subject to intense debate - suggested roles include strengthening the web (the original source of the name), disguising the position of the spider from predators or making the spider look bigger, attracting prey or even making the web more visible for larger animals and so reducing the risk of them walking or flying through it. One large and striking araneid found here in Australia, the St. Andrew's cross (Argiope keyserlingi), shown at the top of this post, gets its name because it builds four stabilimenta radiating from the central hub, while the spider itself sits with the front two and rear two pairs of legs held alongside each other, so the spider itself forms the eponymous cross shape.

Perhaps the most remarkable thing about araneids, however, is that despite the total dependence of most species on their webs for survival, some species no longer make them. The aforementioned bird-dropping spider (Celaenia) is so-called because its lumpy brown-and-white-splotched abdomen really does look like a lump of bird poo, offering excellent camouflage from discerning predators. Instead of constructing a full web, Celaenia simply hang from a leaf or a thread with their legs outstreched. There they catch and feed on moths (excellent pictures of hunting Celaenia can be seen at Esperance Blog). It used to be a mystery how this seemingly limited and haphazard means of capture could possibly feed the spider (after all, how many moths could reasonably be expected to pass by one point over the course of a night) until it was observed that a surprising proportion of the moths being caught (that is, all of them) were males, and that, far from passing by the spider accidentally, male moths will actually approach the spider and remain close by it until caught. It seems that the spider actually emits pheromones that mimic those of a female moth, luring their prey in with the false promise of sexual gratification (like a Trojan virus attached to a spam e-mail). The bolas spiders of the tribe Mastophoreae have refined this process further - as well as producing attractive pheromones, they also dangle a single sticky thread below themselves. When a moth approaches close enough, the spider spins the sticky thread around in the air until it sticks to the moth and they are able to draw it in. How bird-dropping and bolas spiders make their living until they become large enough to handle moths seems a little confused - Brunet (1996) claims that Celaenia construct standard orb-webs until they reach maturity, while bolas spiders produce different pheromones for attracting different-sized moths when at different ages. Forster & Forster (1999) and Yeargan (1994), in contrast, both claim that Celaenia spiderlings produce pheromones to attract psychodid midges. Interestingly, while bird-dropping and bolas spiders are both members of the subfamily Araneinae, it is debatable whether they are each other's closest relatives within the subfamily (Yeargan, 1994), so it is possible that their amazing pheromone-capture techniques could have arisen separately of each other!

REFERENCES

Brunet, B. 1996. Spiderwatch: A Guide to Australian Spiders. Reed New Holland: Sydney.

Forster, R. R., L. M. Forster. 1999. Spiders of New Zealand and their Worldwide Kin. University of Otago Press: Dunedin (New Zealand), and Otago Museum: Dunedin.

Yeargan, K. V. 1994. Biology of bolas spiders. Annual Review of Entomology 39: 81-99.

Spiders Losing their Lungs

Hypochilus petrunkevitchi - photo by Marshal Hedin from Wikipedia.

The current Taxon of the Week arguably has a pretty poor claim on the title, because it is no longer recognised as a valid taxonomic grouping. As I have explained before, modern spiders can be divided into three suborders or infraorders or what-have-you. The Mesothelae or Liphistiomorphae (segmented spiders) are a small group distinguishable from all other spiders by their obviously segmented abdomens. The Mygalomorphae (vertical-fanged spiders) have fangs that move straight up and down, and include the trapdoor and funnel-web spiders and American tarantulas. The largest group of spiders by far is the Araneomorphae (cross-fanged spiders), with fangs angled towards each other, including orb-weavers, cobweb spiders, jumping spiders, wolf spiders, and pretty much any other spider family you're likely to be familiar with. However, some older references may list a fourth group, the Hypochilomorphae, and it's with the latter that we're dealing today.


The Tasmanian cave-dwelling austrochilid Hickmania troglodytes. The four yellow spots visible on the underside correspond to the positions of the book lungs. Photo by Niall Doran from here.

The 'hypochilomorphs' include three small families, the Hypochilidae, Austrochilidae and Gradungulidae, that are now regarded as basal members of the Araneomorphae. Like other araneomorphs, they possess fangs that are angled towards each other rather than parallel. Where they differ from other araneomorphs is in the number of book lungs they possess. Book lungs are the ancestral respiratory structure for all arachnids, and evolved from the gills of their aquatic ancestors as they adapted to life on land. They are little more than gills recessed into the underside of the animal and covered over to prevent moisture loss, and the name "book lung" refers to their appearance in cross-section like leaves of a book. The ancestral number of book lungs in arachnids is four, though many arachnids (particularly the smaller forms, and including some spiders) have independently replaced the book lungs with tracheae, or lack any specialised respiratory structures entirely. Most araneomorphs with book lungs have lost the posterior pair and only have two book lungs. Hypochilomorphs retain the posterior pair, demonstrating their basal position to other araneomorphs and causing them to all too often be damned with the execrable title of "living fossil". However, because this is an ancestral feature rather than a derived one, it does not indicate that hypochilomorphs form a group exclusive of other araneomorphs, and other features make it clear that Austrochiloidea (Grandungulidae and Austrochilidae) are more closely related to the other araneomorphs than they are to Hypochilidae (Griswold et al., 1999). The remaining araneomorphs have usually been presented as a single clade (the Araneoclada), though at least one species of Filistatidae, Kukulcania hibernalis, possesses posterior book lungs as a juvenile, suggesting that family lost the posterior book lungs independently of other araneomorphs, and Lopardo et al. (2004) suggested that Filistatidae may be outside the Austrochiloidea + Araneoclada clade.

The Hypochilidae are large spiders found in Asia and North America. They construct a unique web for snaring prey, often referred to as a "lampshade web" in reference to its shape, though if the description in Forster & Forster (1999) holds for all hypochilids, then the photo on the Wikipedia page for this family is quite possibly upside down. According to Forster & Forster, Hypochilus builds its web on the underside of an overhanging rock, with a tightly woven upper section flaring out around the lower circular edge. Hypochilids are mostly montane species.



The Austrochiloidea are restricted to Southern Hemisphere continents - the Austrochilidae are found in southern South America and Tasmania, while the Gradungulidae are found in eastern Australia and the South Island of New Zealand (Forster & Forster, 1999). The Austrochilidae build large horizontal webs, but many Grandungulidae have abandoned web-building and become active hunters. The Gradungulidae are characterised by the significant increase in size of one of the claws on the legs, which is used to great effect in seizing prey. In one of the Australian web-building species, the cave-dwelling Progradungula carraiensis, a long, sparse web is built between the ground and an overhang, up to and exceeding a metre in height. The spider itself sits head downwards at the base of the web, low enough that the front legs are near the ground. Any suitable prey that walks by the spider is grabbed with the front legs and bitten. The prey may be eaten where it is caught, or carried up to the top part of the web that also serves as a retreat for the spider. One of the New Zealand species, Pianoa isolata, has abandoned the web but hangs down among strands of dense moss, catching its prey in a similar manner to Progradungula. A New Zealand cave-dwelling species, Spelungula cavernicola, shown above in a photo by Paddy Ryan, is an active hunter but often feeds on its prey suspended in mid-air from a silk dragline. The round egg-sacs are also hung from draglines, probably as protection from potential predators.

REFERENCES

Forster, R. R., & L. M. Forster. 1999. Spiders of New Zealand and their Worldwide Kin. University of Otago Press: Dunedin (New Zealand), and Otago Museum: Dunedin.

Griswold, C. E., J. A. Coddington, N. I. Platnick & R. R. Forster. 1999. Towards a phylogeny of entelegyne spiders (Araneae, Araneomorphae, Entelegynae). Journal of Arachnology 27: 53-63.

Lopardo, L., M. J. Ramírez, C. Grismado & L. A. Compagnucci. 2004. Web building behavior and the phylogeny of austrochiline spiders. Journal of Arachnology 32: 42-54.