Larvae turning around in their tunnels

Although borers inside herbaceous stems find themselves constrained in a very tight space, some larvae are able to turn around to face the opposite direction while never leaving their tunnels. I was able to view this behavior in several overwintering larvae by splitting off one side of the inhabited dead stem and covering the resulting opening with an eyeglass lens. This enclosure mimicked the original inner diameter of the borer's tunnel, give or take a millimeter or so, allowing observation of the larva's movement inside the stem. (Once done with my observations, I returned the larva to an intact portion of the same dead stem or taped or tied the original stem piece back together so that the larva could carry on undisturbed.) The following links go to individual pages each with an animated GIF showing a larva in action inside its tunnel.