In late spring and early summer, a plain brown moth lays her eggs on the stem of a tree. She’s a Western Tent Caterpillar Moth (Malacosoma californicum) and this act is the last of her short life.
The cluster of 100-300 eggs is protected from dessication and freezing by a frothy secretion (spumaline) that the mother moth produces from special glands.
The eggs soon begin to develop but do not hatch until early the following spring. After hatching (the entomological term is eclose), the little caterpillars all stay close together and function as a social unit as they feed and grow through the spring.
The group of caterpillars secretes silk to create a web-like structure that we call a tent. The tent is suspended from the branches and twigs of the plant that the caterpillars were born on– the host plant. The caterpillars use the tent as a refuge from cold temperatures and predators. The temperature inside the tent is more stable than that of the surrounding air and can be several degrees warmer.
The caterpillars make forays out of the tent, each one wandering the host plant in search of soft, new leaves to munch on. When a caterpillar finds a good supply of leaves, it eats like crazy, then returns to the tent. It leaves a chemical trail along its path that its siblings can follow to find the new food supply.
All this eating leads to the production of lots of little poo pellets. In the video above, these can be seen as black specks in the silky tent.
Tent caterpillars usually don’t cause any lasting damage to their host plants. On occasion, however, there are population explosions of tent caterpillars and whole forests can be stripped of leaves by the insects. Parasitic wasps and diseases generally keep tent caterpillar populations in check so that these outbreaks are infrequent.
After growing larger and larger for 8 weeks, the caterpillars form cocoons and complete their metamorphosis into adults in about 2 weeks. The adult moths reproduce and the whole life cycle is repeated.