Forest Tent Caterpillars

Written by ABNC’s Visitor & Membership Services Coordinator, Susan Millsap

Tent Caterpillar at ABNC, photo by Susan Millsap

You may have noticed this colorful little caterpillar crawling about recently.  This is the forest tent caterpillar, easily identifiable by the whitish yellow “footprints” and narrow orange and wide turquoise stripes lining its back.  As with most insects, the larvae (called caterpillars in case of moths and butterflies) look very different from the adults.  The forest tent caterpillar is no exception; the adult moths are actually a rather unassuming brownish color.  Some years (like this year) we see more than usual, but this rarely causes significant damage to plants in our area.

These caterpillars, native to most of the United States, spend the majority of their lives as eggs, about nine months.  The caterpillars begin hatching out of their eggs when buds start forming on oak trees and other deciduous hardwoods in the spring. They spend about two months as caterpillars, eating and growing.  Once inside their cocoons, they take about three weeks to emerge as adult moths.  The moths live only about five days, just long enough to lay eggs to continue the cycle.  

The caterpillars are a good food source for songbirds such as robins, blue jays, red-winged blackbirds, and cardinals, as well as bats and other animals.  The adult moths are also a food source for bats, some birds, and other animals.

Tent Caterpillars at ABNC, photo by Susan Millsap

Most tent caterpillars construct “tents” (hence the name) as shelter where they will gather as a group when not feeding.  This provides protection from predators and may also help keep them warm.  Forest tent caterpillars, however, don't actually make tents.  They make silken mats on tree trunks where they congregate en masse between feedings to rest or molt.  It has been observed that these caterpillars respond to threats, including loud noises, by moving their heads from side to side.  This could be an effort to avoid predators or parasites.  

One of the biggest threats to forest tent caterpillars is a parasitic fly commonly known as the “friendly fly” due to its habit of landing on people.  The friendly fly drops its maggots onto the cocoons of the forest tent caterpillars.  The maggots feed on the pupa inside the cocoon, leading to the pupa's demise.  These flies are one of the main controls nature has in place to keep forest tent caterpillar populations in-check.  Rest assured, neither the caterpillars nor the flies are known to bite or sting people.