**Eastern Tent Caterpillars** (*Malacosoma americanum*) are native forest insects known for building characteristic silken “tents” in the forks of trees, particularly in wild cherry, apple, and crabapple species, early in the spring. The larvae feed on the developing foliage, causing noticeable, often severe, defoliation of host trees. While they are unsightly and cause aesthetic damage, they rarely kill healthy, established trees; however, their populations can cycle to extremely high levels, leading to widespread temporary defoliation in forests and orchards.
Taxonomy and Classification
The Eastern Tent Caterpillar is a member of the family Lasiocampidae (tent caterpillar moths) in the order Lepidoptera (moths and butterflies). They undergo complete metamorphosis. They are distinct from the **Fall Webworm** (which builds messy tents at the *ends* of branches in late summer) and the **Gypsy Moth** (which does not build a communal tent).
Physical Description
The **caterpillar** is a large, hairy larva, growing up to $2 \frac{1}{2}$ inches long. Its coloring is distinctive: it is black with a solid, narrow, white stripe running down the center of the back, flanked by dark blue or black spots and light brown or yellow-orange markings. The body is covered in fine, reddish-brown hairs.
The **adult moth** is stocky, reddish-brown to tan, with two oblique white or pale yellow lines running across the forewings. It is nocturnal and seldom noticed, flying primarily in mid-summer.
Distribution and Habitat
Eastern Tent Caterpillars are native to the eastern North American deciduous forests, ranging from the Great Plains eastward. Their habitat is deciduous trees, with a strong preference for the *Rosaceae* family, including wild cherry, apple, plum, and peach. The caterpillars are highly visible in the spring when the foliage is new.
Behavior and Life Cycle
This species has one generation per year. The insect overwinters as an **egg mass**, which appears as a dark, varnish-like ring wrapped around a small twig. The tiny larvae hatch very early in the spring, just as the leaves begin to bud. The larvae are **social** and immediately begin constructing their communal silk tent in the fork of the branches, usually on the sunny side of the tree.
The caterpillars use the tent for shelter, emerging to feed on the leaves during the day. They leave a pheromone trail when foraging to allow the colony to find its way back to the tent. Once mature, the larvae leave the tent and wander to pupate, forming white or yellow cocoons in sheltered places (under bark, on fences, or on buildings). The adult moths emerge in early summer to mate.
Feeding and Damage
The caterpillars are foliage feeders. Their damage is highly visible in the spring as the larvae consume entire leaves and often defoliate isolated branches or entire small trees.
- **Defoliation:** Heavy feeding can significantly reduce photosynthesis, but deciduous trees usually put out a second flush of leaves. The main risk is to young or already stressed trees, or the loss of fruit crops in orchards.
- **Nuisance:** The unsightly nests, and the mass migration of mature caterpillars across walkways, roads, and structures, make them significant nuisance pests during population outbreaks.
Management and Prevention
Control is highly effective when timed properly.
- **Winter/Dormant Control (Best):** Locate and prune out the dark, varnished **egg masses** in winter or early spring before they hatch, then destroy them.
- **Mechanical Removal:** When the tents are small in early spring, use a stick or gloved hand to twist and pull the tent (containing the larvae) out of the tree, then destroy the nest (e.g., place it in soapy water). Do this early in the morning or late evening when caterpillars are inside. **Do not burn the tents in the tree.**
- **Biological Control:** Apply **Bacillus thuringiensis (Bt)** to the foliage when the larvae are small. This stomach poison is highly specific to caterpillars and safe for beneficial insects.
Conservation and Research
As a native species, Eastern Tent Caterpillars are a natural part of the forest ecosystem, though they are managed aggressively in ornamental landscapes and commercial orchards. Research focuses on the cyclical nature of their population outbreaks and the role of natural enemies (parasites and viruses) in regulating their numbers.