• Choose a category
• All
• Classic-Fiction

By Root 761 0

Two days later I climbed back up and found thirty-seven new leaf rolls (presumably made by the more than eighty caterpillars I had released). One caterpillar was being eaten by a shield bug; eight partly rolled (or unrolled) leaves were empty; twelve partly rolled leaves each held a caterpillar, but none of the leaf had been eaten; seven fully rolled leaves with caterpillars inside had some of the leaf eaten; and there were nine clipped petioles. Thus, apparently several of the caterpillars had been eaten; being up in the tree was risky. These were interesting observations, but they could be interpreted in several ways, and no firm conclusion was possible—not enough for a scientific publication. Meanwhile, the caterpillars’ season was over, and I thought about other things.

I did not get an opportunity to think about these caterpillars again until more than two decades later, when I started to write this book and found my notes squirreled away in a file. When I took a break and went for a daily jog during the next ten days in June 2006, I checked for freshly dropped leaf rolls on the gravel under the aspens along the road (in Hinesburg, Vermont). I found 208 of them. Twelve were freshly clipped and nine of these contained a mature larva. (As before, they pupated inside their rolls, and by the first of July the adults, the small gray moths who are fast runners as well as fliers, again emerged.) However, the remaining 196 leaf rolls had petioles (they had not been clipped off ). All but two of these were without a caterpillar. Therefore, caterpillars had left them to make another roll, and they had done so apparently in time, before the tree had shed them.

The leaf rolls I had picked that had petioles but no caterpillars contained piles of caterpillar frass (feces), indicating that a caterpillar had been in residence for a long time, all the while feeding and fouling its nest (or pantry?). The leaf tissue on the inside of the rolls had turned color (yellow) or become necrotic. In short, these rolls had ceased to provide food, and they had been shed by the tree, presumably as a mechanism of getting rid of nonfunctioning leaves. However, before that happened, the caterpillars had left their deteriorating leaf rolls to seek fresh leaves and make a new roll to feed and hide in. That explained why many of the freshly clipped-off rolls that I had found earlier had little feeding damage inside yet contained a large caterpillar.

Apparently caterpillars leave their roll when it fills with feces or becomes necrotic, and then make another roll and resume feeding. As a result, many “empty” rolls accumulate on the trees and these fall off, but late in the summer. Finally, when the caterpillar is nearly mature, it clips off the last roll that it is in, and then rides with it to the ground, where it remains inside, pupates, and then emerges as an adult.

By late August I started seeing leaf rolls of another sort, on young basswood trees. Basswood leaves are gigantic relative to poplar leaves. To a diminutive (microlepidopteran) caterpillar that needs to roll up a leaf to hide in while feeding, a large leaf presents a problem. But these caterpillars had solved it beautifully. Each caterpillar had made a cut into the leaf all the way through several large leaf veins and then up to but not through another major vein. As a result a large portion of the leaf had flopped down while the rest of the leaf stayed up, and the dangling portion of the leaf was then rolled up. The leaf vein from which the roll then hung would continue to supply the nutrients to the rolled-up leaf used by the feeding caterpillar.

I continued to jog almost daily along the same road, enjoying the summer and at the same time keeping track of other signs of caterpillar magic. On 10 September I found out something new about caterpillars that I had never seen or heard about. There was at that time a caterpillar outbreak on the maples (both sugar and red). This outbreak was not as eye-catching as that of the fall webworms (who may enclose whole trees in diaphanous veils of