Yesterday evening I got bored in the house and grabbed the camera to take a walk along the paths. The light wasn't great, but I captured a few interesting shots, including this one of a gorgeous little wasp-like creature feeding on snow-on-the-mountain (Euphorbia marginata).
Going to BugGuide.net, I was able to identify it without too much trouble: an adult poison ivy sawfly. The species name is Arge humeralis. The larvae, which look like caterpillars, feed exclusively on poison ivy, which definitely makes them a beneficial insect in my book. Since we have lots of poison ivy around, I'm fairly confident of this identification.
However, I can't find much other information about the species at all. It's apparently being researched as a potential biological control for poison ivy. One site mentions that the larvae feed gregariously, i.e. in a group, but I could find no real verification of that.
Donald Stokes' book, Observing Insect Lives, talks about sawflies being one of the most primitive types of wasps because they have no stinger and because they are plant feeders. Their ovipositor, or egg-layer, is a small-to-large, saw-like structure - hence the name, sawfly. In sawflies, the ovipositor is used to insert the eggs into plants. In more "advanced" wasps and bees, this structure develops into the stinger that we all love to fear.
I've never seen the larvae, but will definitely be keeping my eyes open for them in the future. Who knows, maybe we'll have insect help in keeping the blasted poison ivy under control in the future!