Walking through the forests of Sands Point Preserve on April 21st, I spied a silken tent pitched upon a black cherry tree sapling (Prunus serotina). The sapling stood three feet tall with a vine full of caterpillars wrapping around. Half of the leaves were eaten.
As I stopped to sketch the hairy black caterpillars with their many blue eyes and what appeared to be one head on each end against the brilliant woven silver star backdrop, I found myself crawling. I knew that some caterpillars are dangerous to the touch, and that some are not; but these caterpillars looked harmless.
I then wondered if this was one of the species of tent-caterpillar that is known to demolish hardwood forests. Conservation biologists urge “early detection, fast response.” In other words, destroy the colony before it has a chance to spread. Concerned, I called my guru in botany, Jason Rosenberg of New Paltz, and he gave me the common sense advice, “just observe them and see what you can learn from them.” Meanwhile dozens of caterpillars were trailing back and forth across the forest floor, and all over me. I kept observing as dozens of caterpillars were following linear trails, probably looking for more fresh leaves, laying down a trail of pheremones.
Doing some research, I found that there are six species of tent caterpillars in North America. This caterpillar happened to be the eastern tent caterpillar (Malacosoma americanum), and not its dangerous stinging and forest-devouring cousin, the gyspy moth (Lymantria dispar), which causes almost a billion dollars in annual damages to the U.S. Nor was it the forest tent caterpillar (Malacosoma disstria), which usually don’t kill the trees they feed upon, unless the trees are already weakened by drought.
Eastern tent caterpillars do little damage to forests; they specialize on trees of the genus Prunus, of the rose family, and these trees are found mostly in plantings of suburban and agricultural areas, with the exception of black cherry trees. Trees of the genus Prunus concentrate cyanide in their leaves as a defense, and the eastern tent caterpillars have evolved to eat the trees and detoxify by spitting out the ingested cyanide in a concentrated juice form.
Today I returned to the tent site. It was a rainy day and the caterpillars were taking a siesta on the underside of their tent. The entire black cherry sapling had been defoliated and as I looked very close, I was able to observe minute new buds where the leaves once were, marking a second spring for the black cherry.
