Friday, April 23, 2010

Eastern Tent Caterpillars

These are the larvae of the Eastern Tent Caterpillar, Malacosoma americanum. It’s a type of moth, so you ought to be calling it the Eastern Tent Caterpillar Moth. That means the larvae in the picture could be referred to as the Eastern Tent Caterpillar Moth caterpillars. It could get sort of confusing. It’s a very pretty creature, but that’s not why caterpillar is so prominently featured in the name.

What draws attention is this structure, most often seen in Wild Black Cherry or related species. This webbed fortress is created cooperatively by the group of caterpillars as a refuge and protection against predation and the elements. Predators would have to penetrate many layers of webbing in order to make contact with the caterpillars. There don’t seem to be many birds or predatory wasps that are up to the challenge.

The caterpillar nest stands out like a flag in the tree. The sight of this web mass can instantly trigger formation of a lynch mob of suburban dwellers ready to protect their homes and families from the evil menace. The incidents I witnessed as a child, always seemed to follow a standard sequence that reminded me of the way the villagers went after the Frankenstein monster. People would gather with their monster fighting tools; most conspicuous of which were gasoline and fire, two items guaranteed to produce a super lawn party. The branch containing the offending nest would be cut from the tree and drug into the open lawn, where the nest was soaked in flammable liquids and set ablaze. It was really fun when the property owner was absent and returned home later to find evidence of the service his neighbors had performed.

Additional web layers are added to the nest as the caterpillars grow. The inside of the nest becomes quite dirty with accumulated frass (caterpillar poop) and shed skins. The caterpillars leave the nest to feed on the tree leaves and then return to the nest. This is what outrages the typical homeowner. A single nest may contain several hundred individuals that can completely strip all the leaves from a medium sized tree. During feeding is when the caterpillars are most vulnerable to predation and many can be lost at this time.

Here are some signs of caterpillar feeding. Fortunately, the caterpillars hatch in early spring and are ready to pupate in four to six weeks. This means that a tree denuded by Tent Caterpillars has time to grow new leaves and is not terribly hurt by the experience. When populations are high, Tent Caterpillars often travel as a group in search in a new food source. Masses of marching Tent Caterpillars also get a response from most suburbanites. I’m unable to watch Cloggers perform without thinking of a community Tent Caterpillar stomping.

1 comment:

  1. YUK--YUK!! I have already seen some tents around. They can clean the leaves of a branch in no time flat!!
    When I was a kid my Dad would wrap a rag around the end of a stick and dip it in kerosene light it and burn out the tents at night when the where all collected there!! We thought that was just great fun!!:>