CATERPILLARS CAN BE FUN TO WATCH

by Whit Gibbons

June 10, 2002

When I asked one of my daughters if I should run an updated version of the following previously published column, she said, "What person who grew up in the South doesn't remember having one of those caterpillars walk up an arm or over their fingers when they put them in the caterpillar's path? Every child should be exposed to caterpillars! I think this may even get some people out there looking at these caterpillars to see if they really follow the silk paths."

I was prompted to recycle the column by my neighbor who claims she does not like to see the tent caterpillars I leave unmolested in trees in my front yard. She insists they crawl to her yard and eat the leaves on her trees. I think she's right that some of my caterpillars visit her yard, but not that they feed on her trees.

Tent caterpillars build their silken nests in early spring in the forks of cherry or apple trees and eat the leaves when they appear. Many people probably feel the same way I once did and my neighbor still does--determined to destroy any caterpillar tents found on such trees in their yard.

This year I found two tent caterpillar nests in the yard in a cherry tree. In former years, I would have decided that the constructed nests and their engineers must go. A gasoline-soaked rag on a long pole could be used to burn the nest, or the nest could be sprayed with insecticide. The first is reminiscent of a gladiator sport; the second releases poison into your yard. Neither is appealing. But I have given up doing this sort of thing anyway. I would rather watch these enterprising creatures.

The eastern tent moth lays her eggs on the tree in early summer and dies soon thereafter. The caterpillars hatch the next spring and become social larvae that cooperate in building the nest and seeking food. They leave the nest during the day, traveling to the ends of limbs to eat buds or leaves. I observed that each caterpillar left a trail of silk when traveling along the limbs. Caterpillars use their mouths to make silk from silk glands, which are modified salivary glands. Other caterpillars passing over the same limb follow the strands of silk left by earlier travelers. These silk highways contain invisible chemicals called pheromones, which are released by many animals for communication of various sorts, leaving road signs imperceptible to humans.

Using their pheromone-laced silk thread, tent caterpillars give notice to their siblings when they find an area on the tree where the eating is good. Experiments have shown that when a caterpillar encounters two thread trails along a limb, it will almost always pick the one along which a well-fed caterpillar has traveled upon its return to the nest, rather than a thread used by an unfed one. Upon finding a source of food, a caterpillar advertises the fact to its nestmates. Electing to spare these caterpillars provides something more fascinating to watching leaves grow on a black cherry tree.

By mid-May the caterpillar numbers appeared to be decreasing and part of the nest in the tree looked destroyed. Did the wrens or brown thrashers that were feeding babies around that time find the perfect food source?

What's left of the old nest is still in the cherry tree but the caterpillars are gone, having moved on individually, each to build a cocoon where it will stay for about three weeks as a pupa and emerge as a small, reddish-brown moth. I'm sure some of those that left made a trip to my neighbor's yard, where they may have been treated ruthlessly if discovered. However, I bet that on the way some served as food for a few birds, lizards, and other animals I would sooner have around than those few extra cherry leaves.

Although it will mean the loss of a few more leaves next spring, I hope some of these backyard visitors make it through the moth stage. The other animals in the neighborhood probably hope so too.



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