Tropical Wasps in Houston!

A tinker bell wasp, delicate and light, seemingly floated on a light mote high under the water oak outside my home office window. I dashed outside hoping to find it, but it would be another year before I could locate and catch one of these lovely tropical wasps. I discovered a nest in the Aspidistra along the fence, and was able to photograph these shy wasps, and send one off to Jim Carpenter, the world expert on social wasps, for definitive identification.

It was Mischocyttarus mexicanus cubicola. Jim had discovered a whole cluster of nests at his brother’s house in San Antonio the year before. And Jim Hunt had caught one at Washington University’s Tyson Research Center in a hanging trap. Where had these lovely wasps come from? It is hard not to enjoy seeing new wasps if you love them as much as we do, but what does it mean? Why and how are they moving North?

The most likely source for the Texas wasps would be Brownsville, Texas, right on the border with Mexico. At about 26 degrees North, it is a fairly tropical place, and we’ve seen other tropical wasps there, like Brachygastra mellifica and Polybia occidentalis. Bird watchers go down there all the time to see tropical species. But this was the wrong sub-species. Jim was able to tell us that by looking closely at the nooks and crannies of her shiny body. This final taxonomic couplet is what allowed him to sort one from the other:

‑               Mid- and hindtibiae more or less dark ferruginous, not yellow and black; wings nearly hyaline; mesosoma mainly black with yellow markings; metasoma black and yellow.

Mischocyttarus mexicanus mexicanus (de Saussure)

‑               Midtibia entirely yellow, hindtibia at most with an ill-defined brown mark; wings considerably yellow-brown; mesosoma mainly ferruginous with yellow markings; metasoma ferruginous and yellow.

Mischocyttarus mexicanus cubicola Richards

Note the author’s name after the species. That tells you who described it. It is also possible in most cases to go to the museum that has that exact specimen, and look at it. I once spent a week learning from Jim, struggling with all the terms, and looking for the details on the tiny wasp bodies. Once you learn them, these characters scream out at you, they are so obvious. I imagine Jim was just being nice not to scream out at me for how clumsy a learner I was. It’s easier to just send him the wasps for identification. And it has the added benefit that they then join the best collection in the world, properly labeled for anyone to study.

The closest place this wasp occurred naturally was in southern Florida. So we supposed that it had come to Texas with the nursery trade. Maybe the increase in citrus in the Houston area would account for it. Now we can grow oranges, lemons, and limes which used to be impossible. But these things are really hard to pin down, so as scientists, we couldn’t say for sure how they got here. With several generations of nests, we guess they are here to stay.

It could be that this species had regularly come into the Houston area, but previously was killed by our winters, even though they are not very cold. Houston is at a latitude just shy of 30 degrees, about the same as Cairo, Egypt. Drive 12 hours south past Ciudad Victoria, but before Tampico, and you hit the Tropic of Cancer, where the sun is directly overhead on the longest day of the year, and it is certifiably tropical.

Now that I think about it, last winter, in January 2009, right around the time of my daughter’s wedding to Julio, it got really cold, into the twenties and stayed there for several days. Maybe that’s why I haven’t seen any tinkerbells this year, but I’ll keep looking.

My first entomology professor at University of Michigan’s Biological Station on Douglas Lake told me that in a research career one could do no better than to choose a group of insects and learn everything you can about it, and follow it for a lifetime. That professor, Jim Lloyd did that with fireflies. I almost did it with wasps, until I took up those lovely social amoebae a decade ago. But I still love wasps in a way the amoebae can never displace. So I’ll be watching for any new invaders, and my ecotourism will be wasp-based.

We published this discovery in Entomologica Americana, or it can be downloaded from my website, Evolve.

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We could just see the wasps peeking out that cool November day.

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Here you can see the long, thin waists of Mischocyttarus, a very neotropical genus.

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The nest was on the underside of an Aspidistra leaf and no longer held brood.

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Jim Carpenter, at the American Museum of Natural History, is the

world-wide expert on social wasps, and he identified Mischocyttarus mexicanus cubicola.

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The AMNH collection of wasps and nests is huge, and is carefully preserved.

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About Joan E. Strassmann

Evolutionary biologist, studies social behavior in insects & microbes, interested in education, travel, birds, tropics, nature, food; biology professor at Washington University in St. Louis
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