Wednesday, October 6, 2010

Wasp Wednesday: Astata

A few weeks ago I wrote about the wasp genus Dryudella. Last week I found examples its sister genus Astata. Both are in the subfamily Astatinae of the family Crabronidae.

The most conspicuous gender in Astata are the males. You can easily spot them in open fields with a little practice. The males of most species perch at the very tips of twigs, or on dried-out flower heads. Their enormous eyes wrap around to the degree that the two meet at the crown of their heads. They are incredibly alert to the slightest motion, and will fly out so fast that they seemingly vanish instantly. They may return to the same perch after investigating the object of their interest, or land on a different perch close by.

The images of the bi-colored male below took persistence and patience to obtain. Knowing the habits of these wasps I simply searched in the immediate vicinity when the wasp left its initial perch. It was only a matter of minutes before it turned up again.

The speed of the males’ flights are enhanced by extra-broad hind wings, another feature that sets them apart from females (females have normal, separated eyes). Whether the males are looking for females from their perches is still unknown, but their “landmark” behavior is reminiscent of the mating systems of other insects. Not all species sit on elevated perches, by the way. A few sit directly on the ground, or on small stones and other objects on the ground.

While the males are showing off their aerial prowess during the late morning and early afternoon hours here in the Sonoran Desert, the females are all business. Each female excavates her own nest, a burrow in sand or soil. I was lucky enough to observe this female (above) initiating such a burrow right before my eyes in a flowerbed at the Tucson Botanical Gardens last Thursday, September 30.

Unlike sand wasps, the females of Astata do not possess a “tarsal rake” of strong spines on their front legs. Instead, they “pull” soil out of the hole they are digging.

What surprised me about the fossorial (burrowing) habits of this wasp was that she eventually disappeared underground altogether. She reached a point at which she never surfaced again. The pile of soil behind her pulsed every now and then as she continued digging, but that was it.

Beneath the surface, the finished nest of Astata is a fairly elaborate, multi-celled tunnel, partitioned with curtains of mud into several chambers in at least some species. The female wasp hunts and gathers the nymphs of stink bugs (family Pentatomidae) as food for her larval offspring. She accumulates several bugs inside the burrow before preparing the next cell.

There are fourteen species of Astata currently recognized from North America north of Mexico, most of them slightly to substantially larger in size than members of Dryudella. Males lack the often white face of their more diminutive cousins. Differences in wing venation separate the two genera more conclusively.

Sources:
Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World. Berkeley: Universithy of California Press. 695 pp.
Krombein, Karl V. et al. 1979. Catalog of Hymenoptera in America North of Mexico. Washington, DC: Smithsonian Institution Press. Vol. 2, pp 1199-2209.

1 comment:

  1. Thank you for your help on this ID. I saw these guys and filmed them at San Pedro river down in Sierra Vista. Amazing critters.

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