Tent caterpillars are a common sight across North America, recognized for the distinctive communal silk tents they construct in tree branches. Their presence is a noticeable part of the spring and early summer landscape in many areas.
The Caterpillar Stage
The tent caterpillar begins its life as a larva, emerging from its egg in early spring just as the host tree’s leaves begin to unfold. These caterpillars are typically hairy, with species like the Eastern tent caterpillar (Malacosoma americanum) being black with a white stripe down the back, brown and yellow lines along the sides, and blue spots. Forest tent caterpillars (Malacosoma disstria) are black, dark brown, or gray, featuring a row of white, keyhole-shaped spots along their backs, flanked by blue and thin yellow stripes. These larvae are voracious feeders, consuming young leaves and growing rapidly over six to eight weeks.
The communal silk tents are built in the crotches of tree branches and are expanded as the caterpillars grow. These silken structures serve multiple purposes, providing shelter from predators and parasitic insects, as well as offering protection from extreme weather conditions, helping the caterpillars regulate their body temperature. While Eastern tent caterpillars construct true tents where they rest and return after foraging, forest tent caterpillars typically create silken mats on branches for resting or molting, rather than a fully enclosed tent. Caterpillars leave these structures to feed and return to them for rest.
The Pupa Stage
Once a tent caterpillar reaches its full size, typically around 2 inches long, it prepares for transformation. The mature caterpillars leave their communal tents and disperse, seeking sheltered locations to pupate. They might find spots on tree trunks, fences, debris, or even under man-made structures.
The caterpillar spins a protective silken cocoon. For Eastern tent caterpillars, these cocoons are typically whitish or yellowish, often mixed with a yellow powder. Forest tent caterpillars also spin silken cocoons, which are yellow and spun within folded leaves or other sheltered places. Inside this cocoon, the caterpillar transforms into a pupa, a quiescent stage where internal reorganization into an adult moth occurs.
The Adult Moth
After approximately two to three weeks within their cocoons, the pupa completes its transformation, and the adult moth emerges. This adult form is what the tent caterpillar ultimately turns into. Tent caterpillar moths are generally stout-bodied and appear dull, often in shades of brown, reddish-brown, or yellowish-brown.
Eastern tent moths typically have a wingspan of 1 to 1.75 inches and are reddish-brown, characterized by two creamy white or pale stripes across their front wings. Females are often larger and paler than males. Forest tent moths are yellow or tan with a thick, furry body, and their forewings feature two distinct dark brown bands. Adult moths possess feathery antennae, but their mouthparts are non-functional, meaning they do not feed during this short-lived adult stage. Their primary purpose as adults is reproduction.
Completing the Cycle
Adult tent moths, having emerged from their cocoons, embark on the final phase of their life cycle: reproduction. Mating usually occurs shortly after emergence, with females laying their eggs quickly. Female Eastern tent moths lay their eggs in a single mass, typically containing 150 to 400 eggs, which encircle small twigs. These egg masses are covered with a dark, shiny, varnish-like substance that protects them from the elements.
Forest tent moths also lay their eggs in masses of up to 300, glued to twigs and covered with a frothy, gluey substance called spumaline. This protective covering hardens and helps the eggs survive harsh conditions. These egg masses overwinter on the branches, with fully formed caterpillars remaining quiescent inside the eggs until the following spring. When new leaves emerge on host trees, tiny caterpillars hatch, beginning the cycle anew. There is only one generation of tent caterpillars per year.