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Sunday, June 14, 2009

Let Sleeping Wasps Clasp

As summer rolls around clouds of these small (6 to 7mm long not counting antennae) wasps gather around certain flowers in the garden. Last year their favorite blooms were limonium latifolium, but this year they seem to favor the apricot cosmos. Around 4pm each day, the wasps begin to settle on the cosmos plants, each grasping the leaf with its mandibles. Once they settle, the body stiffens and sticks away from the leaf at an angle, and so they remain for the night and 1/2 of the next morning at least. The group pictured here numbered about 25 individuals.

I observed these wasps on several overcast days, finding that most or all never stirred until after 11am, and some of them never left their perches. I plucked one of the leaves with wasp attached to observe it without having to bend over the garden fence. The wasp did not move, seeming unperturbed by the movement or possibly catatonic. I manipulated and poked at the leaf a bit, setting it in a window for better light and the wasp finally began to stir. After about 15 minutes of wing spreading and antennae cleaning it finally flew off.

Apparently there are numerous hymenopteran species that display this behavior. Eric Eaton at Bug Eric has an excellent post on his observation of sleeping aggregations in long horned bees and cuckoo bees in Tucson. I concluded that my little friends are likely to be male Cerceris wasps, based on a description at the Great Sunflower Project, and I paraphrase: Cuckoo bees resemble sphecoid wasps, but the wasps have silvery or gold hairs on the lower part of the face while Nomada do not. Also of course bees have branched hairs while wasps' are unbranched. So I chilled one of the wasps and had a look under my pocket scope, confirming the existence of a short golden beard of unbranched hairs on his chin. 5 o'clock shadow?

The female cerceris wasps nest in the soil and provision the nests with beetles (most common) or even bees or wasps. I suppose those would be small to tiny ones given the diminutive stature of this predator.


Moe said...

Wow. What a great post! I have never seen, or heard of, these wasps before.

Bug Eric said...

Great post, great images. Actually, they are male bees in the genus Nomada, easily mistaken for wasps because they are parasitic in the nests of other solitary bees, so lack hair for collecting pollen.

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