Tent Caterpillars Pitch Their Tents

Tent caterpillar tent.

Tent caterpillars have hatched and you’ll see them in saplings everywhere. My father hated these wooly pests and his method was to twist up a newspaper real tight, light it and set the tent-webs ablaze. The caterpillars would fall out, escaping the blaze.

Caterpillar eating a young leaf.

Tent caterpillars are only mildly harmful. They will devour the young leaves on the tree where they have pitched their tent, occasionally they’ll travel far enough to eat leaves on a neighboring small tree, but generally they stay on the tree with their tent.

The caterpillars live in a community and travel in groups to eat.

The the eggs which become the caterpillars were laid by a moth the previous fall, and their hatching is timed so they hatch just as the young, tender leaves are beginning to appear. Once the leaves get larger, the caterpillars have quit eating and gone dormant.

Tent caterpillars are social, going about their daily habits in groups. Appearing in early spring when the weather is much cooler, the tents are built in layers. When the night is cold, the caterpillars all move into a group in one of the inner chambers of the silk web where the temperature can remain as much as 50 degrees warmer than the outside air. They venture to the outer layers in the sunlight as the temperature warms, then during the day they travel in groups into the limbs for feeding. By evening, as the air cools, the caterpillars move back into the web.

Rain crow, or American cuckoo, is a natural predator of tent caterpillars.

The American cuckooo, also known as the rain crow, is the natural predator of tent caterpillars. Cuckoo populations have been on the decline over the past decades due to loss of woods habitat as land is cleared for more farms and house development. (To hear the sound of the American cuckoo, or rain crow, click here for an audio clip).

Bacillus, sold under the brand name of Thuriside.

Setting the web ablaze may be satisfying, but it can also damage the branches of the tree. A less harmful method is to the spray tree foliage with a Bt mix (Bacillus thurenginsis, the same organic control we use for cabbage loopers and other caterpillar pests). It’s non-toxic and not harmful to other insects. They have to eat and digest it for it to work, so spraying the leaves of the tree is helpful.

Tent caterpillars look messy but they don’t do a lot of serious damage. They prefer wild cherry, persimmon or fruit trees and seldom move far from the tree where their tent is located. While it may look like they are spreading to other trees, those are usually completely different colonies where other moths have laid their eggs.

Caterpillars grow fast and typically complete their development in seven to eight weeks. They leave their tree and move to the ground or under the eaves of buildings to spin their cocoons. About fourteen days later the moth emerges and begins laying eggs for the following spring.

Happy spring (or is that summer?)