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October 10, 2013 / Rae Spencer

Kleptoparasites

Wasp Sept 7

The tree in our front yard had fewer caterpillars this summer, so the yard had fewer thread-waisted wasps. Instead of a daily swarm of wasps under our tree, I saw one or two a week.

Wasp Sept 7

The wasps dug burrows as usual, but I didn’t see any of them return to their burrows with prey.

Wasp Sept 11

Twice I waited over an hour as wasps searched through leaf litter on the ground and branches overhead. Both times the wasps were still hunting when appointments called me away.

Wasp Sept 11

My wasp failures were disappointing, but it’s always worthwhile to spend a few hours sitting quietly in the yard. Last year as I waited on the wasps, I found a wolf spider carrying her army of spiderlings. This year I found flies.

Fly Sept 11

The flies caught my attention because they seemed as interested in the wasps’ activity as I was. They watched as intently as I did.

Fly Sept 11

As the wasps dug, three or four flies positioned themselves within a few inches of the developing burrows. Each time a wasp carried a pinch of excavated dirt away, the flies zoomed in and flew quick figure-eight patterns over the burrow. When the wasps returned and resumed digging, the flies lit nearby and watched until the wasps left again.

Fly Sept 11

The longer I watched, the more convinced I became that the flies were kleptoparasites. They were waiting to deposit their larvae in the wasps’ larder, alongside the wasps’ hungry larvae.

Fly Sept 11

The behavior is well-documented. It’s one of those complicated, clever twists of nature that fills me with questions. How do the flies learn to follow the wasps? Generation after generation, flies see a thread-waisted wasp and something whispers deep within their experience. Follow it. And they obey. Why?

4 Comments

  1. jeanryan1 / Oct 10 2013 8:07 PM

    We have a neocortex, they have knowing. We grope our way along, they are born ready.

    I admire your abiding love for this world.

  2. yakinamac / Oct 11 2013 9:51 AM

    Fascinating stuff – and the photos are just brilliant. Thank you for sharing your observations.

  3. Fictionquest / Oct 14 2013 10:13 PM

    you must have extrordinary patience! Very nicely done.

  4. bardessdmdenton / Oct 17 2013 2:37 PM

    As always, wonderful photograph and interesting, beautifully written commentary, Rae. XO

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