Found in the order Lepidoptera, which is moths and butterflies, the tent caterpillar adults are light brown with stout moth bodies and a wing span of an inch and one half. Their shiny white web nests can be found in the in the forks of shrubs or tree branches and are the only such webs found in early spring. Of all the phases of a tent caterpillars life cycle the simplest to find and most interesting to observe is the larval phase.
The larvae are found primarily on apple or cherry trees and begin to emerge just as the first leaves are showing. All the caterpillars that have hatched help with the nest building which is made of tough layers of silk with spaces between each layer and continuous sheets of webbing that go around the entire nest. Each nest has one or more opening so the caterpillars can come and go. The best time to observe the caterpillars working on their nest is during the mid-morning hours and during the early evening.
Although the purpose of this webbed nest is unclear it is believed that it may provide protection from predators as well as a moist, warm environment to foster the growth of the insects. From time to time the caterpillars can be seen on the outside of the nest in groups perhaps warming themselves in the sunshine after a cold night or cooling down when its hot and humid. They will also leave the nest three times each day to feed with the longest period being at night.
As they exit the nest each will leave a long trail of silk on the twig where they exit to mark their way back to the nest. These trails can be clearly observed in the most traveled areas. It is also believed that the silk trails are used to relay information to other caterpillars such as where the best sources of their food supply can be found. The caterpillars will continue working on the nest until they have molted five times. During each molt, there will be a two day period of inactivity while each insect sheds its skin. Cold or rainy weather will also interrupt their activity.
When the caterpillars are preparing to leave the nest to pupate, they will most commonly crawl to the end of the branches flicking their bodies off or descend on a silk thread. During this time they can be observed crawling about in search of a place to pupate. They may even be observed moving in masses across highways with cherry or apple trees on either side. Once they have found a safe area such as under a log or in a bark crevice, each caterpillar will weave a tough cocoon that is half as long as its body.
It will then excrete a yellow substance that hardens the cocoon and dries to a powder that when disturbed drifts in the air much like chalk dust. The new moths will emerge during the midsummer months to mate and deposit their egg cases by late summer after which they die. The egg cases are dark, shiny masses that surround a twig. Less than one inch long the egg cases are water-resistant with a hard, bubbly appearing substance covering the eggs. These will remain on the twig where they were laid unhatched until the following spring.
In the caterpillar stage of their life, there are parasites that prey on the tent caterpillar. The tachinid fly, which looks like a large house fly, is known dart into the nest laying its eggs behind the head of each caterpillar. When the eggs hatch the fly larvae feeds on the caterpillar. As a defense, the tent caterpillar can be observed flicking its head when this predator approaches or moving inside their nest.