Migrant hawkers scramble competition

I'm used to watching migrant hawkers foraging over gardens, leafy streets and sheltered woodland rides, some times in groups. They are immature individuals, gathering energy away from water. Migrant Hawkers, unlike other hawkers, mature slowly, and will move to suitable breeding sites after their long immature period. During this past week I've watched them in their breeding sites in lakes and drains, where mating and egg-laying takes place.

A mature male rests briefly between bouts of searching (Pickering Park, 27th August) 

Males at the breeding site 
At one of my local parks (Pickering Park) last week, dozens of Migrant Hawkers sat or patrolled alongside marginal vegetation around the lake. The males, now fully mature and showing their bright blue spots and eyes and side yellow-green stripes often hovered in a spot, or explored the vegetation, flying well into it, searching for females.

A typical hovering male in a clearing at the marginal vegetation (Pickering Park, 27th August), offering them good views.

Mating
I saw no females, until one was captured by a male: no preliminary or courtship, the male just tackled her and positioned himself to grab her by the head. The female is then able to curve her abdomen and mate, retrieving sperm from the male's secondary genitalia at the base of the abdomen, forming the 'wheel position'. They may fly in wheel position very fast, zigzagging alongside the marginal vegetation edge or briefly rising into the air, before settling on vegetation (above).

Ovipositing female (Foredyke Stream, 1st September)

The moment when the male passes by, and sees the female.

The pair, mating.

Oviposition
A couple of days ago I watched a patrolling male on a ditch doing its usual patrolling routine, rising to inspect any passing individual, even paying attention - briefly rising - to birds flying over. A mated female arrived, unnoticed, and started laying eggs on live leaves well above the water line, I'd say over one metre over the water. She checked leaves and unsheathing her ovipositor, started laying into them (the eggs will overwinter inside the plant leaves, where they are protected from predation). After a couple of minutes, the male noticed her, tackled her and mating ensued. This time the pair settled briefly on plants, which allowed me to take a shot (above). Mating in Migrant Hawkers is longer than in other territorial relatives.

Two males resting near each other (Pickering Park, 27th August)

Nonterritorial males
This species is notoriously non-aggressive, even at the breeding sites. Males will even rest within view from each other (above). A patrolling male will swiftly rise to check a passing one, but the interaction is suggestive of them 'checking' that they are not a female, and letting the other individual go their way if it's a male. There is no defended territory, just males congregating on suitable ovipositing sites and searching for females, a type of mating tactic called 'scramble competition'. This appears to be the reason behind the long copulation. A territorial male mating for a long time may lose the territory to an invader, or miss extra mating opportunities. A nonterritorial male has less to lose, and therefore makes sure that he fertilises as many as possible of the females' eggs, possibly by taking time to remove any previous sperm before transferring his transfer. These patterns have been shown to stand when the copulation duration of territorial and nonterritorial drogonfly species were compared, but I haven't found specific data on the Migrant Hawker. To illustrate the pattern, the Emperor, a territorial species, copulates for an average of 10 min, while the Common Hawker, a non-territorial one, copulates for an average of 67 min. Of course, this lengthy copulation is not necessarily to the benefit of the female, who may be already mated, as the female already laying eggs, and therefore this sets the stage for the evolution of female counter-tactics, such as visiting the water as little as possible and avoiding males if they can, something I have covered before at Bugblog.

More information
Córdoba-Aguilar, A., Serrano-Meneses, M. A. and Cordero-Rivera, A. Copulation Duration in Nonterritorial Odonate Species Lasts Longer than in Territorial Species. Ann. Entomol. Soc. Am. 102, 694–701 (2009).

Do adult female house spiders roam?

As you gather from my last post, it is quite common to come across adult male house spiders, Tegenaria, roaming in search for females in late summer and autumn. Females are supposed to wait for them at the bottom of their web funnels. I was puzzled to find this fully grown, beautiful female inspecting my cat scratching post, in the open, an hour ago. Do females roam too?

The very pregnant spider

 Most of the very abundant female wolf spiders in the garden (Pardosa sp.) are looking like the one above: their distended abdomen indicating they are about to lay eggs. I only saw one was already carrying an egg sac, the first of the year, sunbathing on the fence.

Wool-Carder Bee watching 2: The female

The first time I came across Anthidium manicatum, the Wool-Carder Bee was after hearing it, not the usual humming noise bees make when flying, but that produced by a female's jaws cutting the hairs of a plant I had recently planted in the garden, Lamb's Ears (Stachys byzantina). Since then, this has been a plant that has not been missing from the garden, just because it is a sure way of attracting Wool-Carder bees. The contrast between male and female's behaviour couldn't be more stark. Female wood-carder bees get about their business bothering no other insect, they are even quite shy and easily disturbed. They emerge more or less at the same time than males, sometime in June and set about nesting in some pre-existing cavity. Their cottony nests were described in the early 20th century by the French entomologist, Jean Henri Fabre in his book 'Bramble Bees and Others' as 'by far the most elegant known specimen of entomological nest-building'. Fabre was a curious naturalist, especially fascinated by bee nesting habits and encouraged solitary bees to nest in reed stems and glass tubes so that he could observe them in action.
Fabre described the female carding behaviour in vivid detail:

"Faithful to the plant recognized as yielding good results, the Anthidium arrives and resumes her gleaning on the edges of the parts denuded by earlier harvests. Her mandibles scrape away and pass the tiny fluffs, one by one, to the hind-legs, which hold the pellet pressed against the chest, mix with it the rapidly-increasing store of down and make the whole into a little ball. When this is the size of a pea, it goes back into the mandibles; and the insect flies off, with its bale of cotton in its mouth."

But this striking behaviour had not escaped notice of one of the most observant and meticulous recorder British naturalists in the 18th century, Gilbert White, who wrote in 'The Natural History of Selborne'

Female wool-carder bee scraping the cotton away

She rolls the cotton into a ball

The ball of cotton is now finished

And the bee flies away with it to her nest

This is the Stachys byzantina, still intact today, waiting for the shaving of the bee.