Thursday, July 5, 2012

Wasp Wednesday: Stizoides renicinctus

One of the cool “surprise bugs” from the ”wasp tree” was a kleptoparasitic wasp (I’ll explain that term below), Stizoides renicinctus. This insect is so obscure that it has no common name in English, but that doesn’t take anything away from its unique life history.

S. renicinctus is one of only two species in the genus occurring in North America. Globally, there are thirty species in the genus, most found in Africa, Mediterranean Europe, the Middle East, and India. The only other species in the U.S. is S. foxi, restricted to Arizona (and south into Mexico).

Field marks that help to identify S. renicinctus include an all black body with a red or orange band on the second dorsal abdominal segment (tergite), dark wings with translucent wingtips, and an overall elongate appearance. Both genders are nearly identical in appearance and size, at about 16-18 millimeters.

One usually encounters the males taking nectar from flowers. I was surprised at the fair number of them on the saltcedar tree during the latter half of June here in my Colorado Springs neighborhood. I have also seen this species in southern Arizona, coming to the blossoms of Seepwillow, Baccharis salicifolia in dry arroyos or along rivers.

Females are mostly busy seeking hosts for their offspring. The term “kleptoparasite” refers to an animal that essentially raids the refrigerator of its host organism. That means the parasite feeds on the material stored as food by its host. S. renicinctus is known to exploit the food caches of other solitary wasps in the genera Prionyx and Palmodes. Female Prionyx hunt grasshoppers (Acrididae), while Palmodes hunts katydids (Tettigoniidae). The wasps dig burrows and stock at least one prey item per cell that a single larva will consume to grow and mature into an adult wasp of the next generation. The female Stizoides renicinctus locates the closed burrow of a host, digs it open, destroys the host egg, and replaces it with one of her own. The larva that hatches will eat the food the host mother wasp took such care in providing.

It has been noted that S. renicinctus is not always solitary. Individuals will gather in “sleeping” clusters on vegetation at night. They apparently do this in the face of impending inclement weather, too. I found a loose aggregation forming in the saltcedar bush on the afternoon of June 16 as storm clouds began to gather. These wasps will sometimes be found amid sleeping clusters of other solitary wasps as well.

These wasps are quite efficient parasites, as documented by I. LaRivers in a 1945 paper in American Midland Naturalist. He found the species parasitizing Palmodes laeviventris in Elko County, Nevada. The Palmodes were doing local agriculture a service by slaying Mormon crickets (a type of wingless katydid), but the Stizoides wasps were also reaping the benefits. LaRivers estimated a parasitism rate of about 7.5 percent, which he extrapolated to roughly 10,000 destroyed Palmodes nests in about 350 square yards.

Ok, so Stizoides is an outlaw of the Old West (it actually ranges from Michigan and Wisconsin south to North Carolina and west to Alberta, British Columbia, California, Arizona, and Mexico). I would like to think that seeing a good number of specimens means that there is also a thriving population of host wasps. That in turn means abundant grasshopper prey, and thus a healthy habitat.

Be on the lookout for Stizoides where you live, and see if you can find one in the act of finding a host. You may discover a relationship previously unknown to science. You just never know.

Sources: Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World: A Generic Revision. Berkeley: University of California Press. 695 pp.
Evans, Howard E. and Kevin M. O’Neill. 2007. The Sand Wasps: Natural History and Behavior. Cambridge, Massachusetts: Harvard University Press. 360 pp.

14 comments:

  1. they actually look friendly
    ...for wasps ;)

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  2. I think I have this bug in my yard. Many of them. Flying low to the grass all day. I also have one nestled into a near opening sunflower head (small 2.5ft one). But I live in Florida. Is it possible this is the same bug? I have some pics on my cell phone. I can email them if it will help. They aren't great.

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    1. What you are describing sounds like males of the Blue-winged Wasp, Scolia dubia. Good to have because they kill the "white grubs" that eat the roots of your lawn grasses.

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  3. I wonder if that parasitism rate of 7.5% is an EES? A higher rate might drive the parasitised species numbers down and make them harder to find? So by distributing her eggs amongst a number of different species she can maintain them all at a high rate.

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  4. Saw one today on a pile of logs for our wood burning stove that still need cutting. This wasp was not intimidated by me in the least. Are they as aggressive with humans, dogs, cats and birds as they are with the other bugs who's hives they take over? P.S.:I'm in the Northeast, didn'the see any states in this area noted as being home to this wasp.

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    1. Yes, these are western wasps, so I strongly suspect you are describing something different.

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    2. I live in a Syracuse, NY suburb and saw one of these today on one on my bushes. It looked to be 'mounted' by another flying insect that resembled what a mosquito larvae (ml) looks like. Another ml was attacking the first one to, I assume, mount the wasp. The wasp was black with a distinctive orange stripe.

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    3. Ed: This species does not occur in New York state. You were observing something else; and while I have suspicions about what you describe, without images, video, or my own firsthand observation, I am reluctant to speculate.

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  5. Saw one today with a green cricket or grasshopper in its clutches. Just outside of Augusta Georgia.

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    1. You saw something else then, maybe a Tachytes sp. Please read the blog, this particular wasp is a kleptoparasite of other wasps. It does not hunt its own prey.

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    2. Live and learn! It was really cool whatever it was....

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  6. I have these in my yard and live in CT. Are they stingers? Should be sting allergic people be concerned?

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    1. This species is not found in Connecticut. Yes they can sting, but being solitary they are not defending a whole nest full of vulnerable larvae and pupae. I think you are probably seeing males of Scolia dubia, which are likewise solitary.

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  7. This wasp is found in CT. I found two in my school yard. It was the completely black with one single orange stripe on it

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