Wednesday, March 28, 2012

Wasp Wednesday: Spilichneumon

One of the more common early spring wasps here in the Front Range of Colorado is an ichneumon wasp in the genus Spilichneumon. According to the Database of Hymenoptera in America north of Mexico there are at least four species in the state, so perhaps I am seeing more than one.

These wasps are active and skittish enough that they defy my ability to get really crisp images of live specimens, but I have found two deceased individuals on bike trails here in Colorado Springs. Plus, my fiancée found one at the Cheyenne Mountain Zoo. This specimen is shown below.

These wasps overwinter as adults, inside rotten logs and other protected situations, so they are among the first wasps one is likely to encounter by winter’s end.

Members of the genus Spilichneumon are not well-known, at least in the western U.S. The global range of the genus is the northern hemisphere (termed “holarctic”), and Oriental. Here in North America, most species are found in the extreme northern U.S., Canada, and Alaska, and along major mountain ranges as far south as Arizona.

This is yet another wasp you can count among your friends. Spilichneumon is an internal parasite of noctuid moth caterpillars. The female wasp finds a caterpillar and injects a single egg into it. Her larval offspring then feeds inside the caterpillar, allowing the host to eventually graduate to its pupal stage. The wasp larva pupates inside the host and emerges from the host chrysalis as an adult wasp.

I wonder if Spilichneumon competes with the cutworm-hunting sphecid wasps in the genus Podalonia? Both go after the same prey, at least in part, but Podalonia appears to be far more abundant here than the ichneumons. My observations may be biased, however, since I am usually out at the warmest part of the day, when Podalonia is most active. Spilichneumon, and other genera in the subfamily Ichneumoninae, tend to shun extreme heat and direct sunlight.

Look for this genus where you live. See Bugguide for better images. Look on the forest floor in open woodlands, as the wasps tend to seek their prey among leaf litter.


  1. Another species to count among my friends...As a kid, between 4 and 5 years old, I tried to raise some caterpillars, but instead of butterflies I got a bunch of little barrel shaped cocoons and an awfully shrunken caterpillar. The experience turned me off this kind of entomology for a long time. Right now I'm trying to photograph caterpillars and again to raise them to see the adults. I like ichneumons, too, but...(:

  2. I'm delighted to find your essay. I photographed one of these and was having difficulty learning more about them.

  3. Thanks Eric! This confirmed my suspicion of their aversion to light. I found one this May near Anaconda, MT and she wouldn’t stop moving until safely under a rock, making it difficult to photograph.


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