Wednesday, July 13, 2011

Wasp Wednesday: Therion morio

Unfortunately, here in the Sonoran Desert of southern Arizona, there is not a great diversity of ichneumon wasps, at least not the larger, more colorful species that one finds routinely in the deciduous forests of eastern North America. I was delighted to find a female specimen of Therion morio at the Vernon Wildlife Area near Mukwonago, Wisconsin on June 25. Even more amazing, it actually paused long enough for me to snap a few images. The one below is the best of the lot in the dim light of the forest understory.

This species is about the size of a black and yellow mud dauber, and it would not be surprising to find it is indeed a mimic of Sceliphron caementarium. The rule of thumb with ichneumon wasps is that if it looks like a stinger, then it isn’t a stinger. Such is the case here. The female has a short, spine-like egg-laying organ called an ovipositor. She does not use it in self-defense, only to inject eggs into caterpillars.

The larvae of this wasp are internal parasites of moth caterpillars, including the Fall Webworm, Hyphantria cunea, so this ichneumon should be considered a beneficial biological control of such pests. Other recorded hosts include the larvae of other tiger moths (family Arctiidae): Cycnia inopinatus; the Virginia Tiger Moth, Spilosoma virginica; the Saltmarsh Caterpillar, Estigmene acrea; and the Spotted Tiger Moth, Lophocampa maculata. While the wasp’s egg is laid in a caterpillar host, the adult offspring will emerge from the moth’s pupal stage.

Therion morio, which has no common English name, is a widespread species ranging from Nova Scotia south to Florida and west to Washington, northwest Nevada, southeast Kansas, and Mexico.

Sources: Carlson, Robert W. 2009. “Ichneumonidae,”


  1. I just came across one in Aurora, CO! Thanks for helping me identify it. I'm worried this particular one is injured because its wings aren't working properly. Just keeps climbing around but can't lift off. Poor thing. Sure is beautiful to watch, though!

  2. Great Information. Thank you.


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