A Sinister Collection?

If you've never dared to look closely at wasps, here's a bit of what you've been missing:

Euodynerus castigatus, Illinois Beach SP, Lake Co., IL  6/7/2012

Stenodynerus oculeus, Illinois Beach SP, Lake Co., IL  7/21/2013

These two species are in the family Vespidae, which also includes the familiar Paper Wasps, Yellowjackets, and Hornets.

Great Golden Digger Wasp (Sphex ichneumoneus),
Illinois Beach SP, Lake Co., IL 9/16/2012

This one's in the family Sphecidae.

Dolichomitus irritator, Illinois Beach SP, Lake Co., IL  11/11/2011

Protichneumon grandis, Necedah NWR,
Juneau Co., WI 8/10/2013

And these two are in the most diverse family in the order, the Ichneumonidae. (Estimates for the number of species worldwide range from 60,000 up to 100,000!)

These are just a few of the 18,000 species of hymenopterans estimated to occur in North America. (1) Given that most of them are nectar feeders, and clearly compete with each other, how do so many species manage to coexist?

Well, it turns out that many of them are only nectar feeders as adults. Most of the wasps are parasitoids -- as larvae, they eat insects or other arthropods that their mother provides, first paralyzing them with her sting. In some cases, those other arthropods can include spiders, even large ones! Many wasps are extremely host-specific (i.e. they only attack one or a few critters) as well, and since there's so many other arthropods, there's lots of possible niches to fill. (2)

Their use of pheromones as sexual signals means that two species can coexist without any obvious morphological differences between them, and it's probably not surprising that we find many cryptic species complexes in the smaller wasps. In many cases, what was at first thought to be a single, generalist species has turned out to be multiple, nearly identical specialist species. (3)

I find all this stuff fascinating on it's own -- the richness of our natural world never ceases to amaze, and it just gets better as you look closer. But there are practical advantages to learning about diversity in these wasps: many of them are used for biological control of pest insects, and knowing what's what with the wasps and their hosts can be the difference between an effective control program and a total waste of time and money. (4)

The next time you get the chance to stop and smell the roses, look out for little visitors, and take a moment to think about how delightfully intricate the world can be!

(1) http://bugguide.net/node/view/59

(2) Hawkins, B. A., LaSalle, J., & Gauld, I. D. (1993). Refuges, host population dynamics and the genesis of parasitoid diversity. Hymenoptera and Biodiversity., 235-256.

(3) Bickford, D., Lohman, D. J., Sodhi, N. S., Ng, P. K., Meier, R., Winker, K., ... & Das, I. (2007). Cryptic species as a window on diversity and conservation.Trends in Ecology & Evolution, 22(3), 148-155.

(4) Rosen, D. (1978). The importance of cryptic species and specific identifications as related to biological control. In Beltsville symposia in agricultural research.(2). Biosystematics in agriculture. Invited papers presented at a symposium held May 8-11, 1977 at the Beltsville Agricultural Research Center (BARC), Beltsville, Maryland 20705. (pp. 23-35). Allanheld, Osmun & Co. Inc..