Friday, August 13, 2010

Not a caterpillar...

On Sunday, I helped lead a field trip with Rick Gardner, a.k.a. Rico Suave, for the Midwest Native Plant Conference to Gallagher Fen. Gallagher Fen is an amazing place and I will have some more about that in a later post.

While we were there the previous day on a scouting trip, we found what looked like a crazy caterpillar. I, at first, wondered if it had woolly aphids attached to it, but later figured out that was not correct. (Harvester caterpillars do so to fool ants that protect the aphids. You can read more about that here.) I also soon realized it was not a caterpillar at all. It was a sawfly larvae. Sawfly larvae can be identified by counting the prolegs on the critter, the fleshy feet that are behind their six true legs. Caterpillars, larvae of moths and butterflies, have six true legs and five or fewer pairs of prolegs. Sawfly have six true legs and six or more pairs of prolegs. It will usually look like a sawfly has legs continuously down the length of its entire body.

Photo by Scott Hogsten

Why is it called a sawfly? This photo shows the ovipositor or egg-layer of the female sawfly. It looks like a miniature saw. The female will saw a small slit into a leaf and lay an egg. When the young emerge, they will feed on the leaves. The young prefer butternut and walnut tree leaves, and will occasionally feed on hickories.

After searching BugGuide, I found out it is a Butternut Woolly Worm. It will turn into this lovely sawfly with a shiny black body and white legs. The white extensions are a waxy secretion. I couldn't find out much about the secretion to see if it was bad tasting or had defense properties, but I will keep looking. Very strange creature!


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