Tent Caterpillar

Tent caterpillars are moth larvae that belong to the genus Malacosoma in the family Lasiocampidae. There are about 26 species of Malacosoma in North America. Still, the most common are the Eastern tent caterpillar (Malacosoma americanum), Western tent caterpillar (Malacosoma californicum), and Forest tent caterpillar (Malacosoma disstria).

Host Plants

Tent caterpillars are not very picky about their food. They are known to feed on a variety of trees, including but not limited to apple, cherry, peach, pear, and plum (Prunus spp.), ash (Fraxinus spp.), birch (Betula spp.), willow (Salix spp.), oak (Quercus spp.), maple (Acer spp.), poplar (Populus spp.), and many others.

Regions impacted

Tent caterpillars are found throughout North America. Their presence varies from year to year; some years there may be few, while in other years, there may be large outbreaks.

Description

Tent caterpillars are easily recognized by their silky, tent-like communal nests in the branches of host trees. The caterpillars are hairy, about 2 inches (5 cm) long when mature, and often brightly colored with blue, white, black, and orange markings. The adult moths are typically brown and nondescript, with a wingspan of about 1.5 inches (4 cm).

Life Cycle

Tent caterpillars go through a complete metamorphosis. Their life cycle includes four distinct stages: egg, larva (caterpillar), pupa, and adult (moth).

• Egg: Adult female moths lay clusters of eggs on suitable host trees during the summer season. The eggs are laid in masses and covered with a frothy, protective substance that hardens over time. This egg mass is attached to a tree branch. The eggs remain dormant through the fall and winter months, and hatch in the spring, timed with the budding of leaves on their host trees.
• Larva (Caterpillar): Upon hatching, the larvae, or caterpillars, start to build a silk tent in a fork of the tree branches. This tent provides them protection and is continuously expanded as the caterpillars grow. The caterpillars are social and live together in these tents, venturing out to feed on leaves during warmer parts of the day. When not feeding, they return to the safety of the tent. The caterpillar stage lasts for approximately 4 to 6 weeks, during which the caterpillars go through several instars, or growth stages, shedding their skin and growing larger each time.
• Pupa: After reaching their full size, the caterpillars move away from the communal tent to find a suitable place to pupate. Each caterpillar spins a cocoon around itself and transforms into a pupa. In this stage, the caterpillar undergoes a radical transformation, reorganizing its body into the form of an adult moth. This stage can last two weeks or more, depending on environmental conditions.
• Adult (Moth): The fully formed adult moth emerges from the cocoon. The adult moth is generally nondescript in coloration, often a brownish hue that provides camouflage. Once emerged, the adult moths seek mates. After mating, the females lay their eggs on a host plant, starting the cycle anew.

Throughout their lifecycle, tent caterpillars are subject to various threats, including predation, parasitism, and environmental conditions. Their cyclical outbreaks and significant defoliation of trees can make them a nuisance, but they are a natural part of many forest ecosystems.

Damage and Detection

Damage

Tent caterpillars are known for their substantial appetites and can cause significant damage to a variety of trees. The damage caused by these insects is primarily defoliation. Caterpillars consume the leaves of the host trees, often resulting in extensive or even complete defoliation of the tree during severe infestations.

While healthy trees typically can survive such defoliation and regrow leaves within the same season, repeated infestations can stress the trees and make them more vulnerable to diseases and other pests. Weaker or young trees may not recover from the defoliation.

For fruit trees, a severe infestation can impact fruit production. If the leaves are eaten early in the season, the tree’s ability to photosynthesize is reduced, which can result in smaller, less plentiful fruit.

Detection

Tent caterpillars are fairly easy to detect due to several distinctive signs:

• Silk Tents: The most recognizable sign of tent caterpillars is the presence of their silk tents. These are typically found in the crotches of branches on host trees. The tents start small but can become quite large with the growth of the caterpillar colony.
• Defoliation: Patches of missing leaves or entire defoliated trees can indicate the presence of tent caterpillars.
• Caterpillars: The caterpillars themselves are also a clear sign. They are usually spotted on the trunks and branches of trees, particularly near their silk tents. Depending on the species, they can be various shades of blue, black, or brown, often with distinctive hair patterns or stripe patterns.
• Frass: Frass, or caterpillar droppings, can often be found beneath infested trees.

The best time to detect and manage tent caterpillars is early in the spring when the caterpillars are still small, the tents are less developed, and the potential for damage is reduced. By monitoring trees regularly, particularly known host species, you can detect them before they cause significant damage.

Prevention and Control