Kansas State University

–by Dr. Raymond Cloyd

European pine sawfly, Neodiprion sertifer

Spruce spider mite, Oligonychus ununguis

Lilac/ash borer, Podosesia syringae

— Dr. Raymond Cloyd

The larvae (caterpillars) of the Eastern tent caterpillar, Malacosoma americanum, are emerging (eclosing) from their eggs and feeding on the leaves of trees and shrubs (Figure 1).

Figure 1. Eastern tent caterpillar feeding on new leaves (Raymond Cloyd, KSU)

After caterpillar’s emerge from the eggs, they create a distinct white, silken nest (or tent) in the branch crotches of trees and shrubs (Figure 2) including: birch, crabapple, hawthorn, mountain ash, poplar, willow, and flowering cherry, peach, and plum. The nest protects caterpillars from cold temperatures and natural predators.

Figure 2. Eastern tent caterpillar nest (Sean Mills)

Caterpillars are black and have a white stripe extending the length of the body along with blue markings on both sides of the body (Figure 3). There are five larval instars (stages between each molt). Eastern tent caterpillar is one of our earliest caterpillar defoliators in the season, feeding on newly emerged leaves, which can reduce the ability of trees and shrubs to produce food by means of photosynthesis. Although feeding damage may not directly kill a tree or shrub, a decrease in photosynthesis can predispose plants to secondary pests such as wood-boring insects. Leaf quality can influence tree and shrub susceptibility. For instance, black cherry, Prunus serotina, trees grown in the shade are fed upon less by Eastern tent caterpillars due to lower leaf nutritional quality.  

Figure 3. Eastern tent caterpillar (Raymond Cloyd, KSU)

The young or early instar (1^st through 3^rd) caterpillars are active during the daytime and reside in the silken nest at night. During the day caterpillars emerge from the silken nest and feed on plant leaves. On over-cast or cloudy days caterpillars will remain inside the silken nest. The final instar (5^th) caterpillar only feeds at night. The length time of time that caterpillars spend feeding increases 4-fold between the 1^st and 5^th instars. Feeding activity depends on temperature with caterpillars feeding for a longer period of time when exposed to warmer temperatures than cooler temperatures. Eastern tent caterpillar overwinters as an egg mass attached to the branches or small twigs (Figure 4). There is one generation per year in Kansas.

Figure 4. Eastern tent caterpillar egg mass attached to branch (Raymond Cloyd, KSU)

The silken nests can be physically removed or disrupted by hand. You can destroy, disrupt, or open-up the silken nest using a rake or a high-pressure water spray. The young exposed caterpillars are susceptible to consumption by birds. However, the later instars are fed upon less because the hairs on the body deter birds from feeding on them.

Spray applications of the bacterium, Bacillus thuringiensis subsp. kurstaki, or spinosad are effective in killing small (young) caterpillars and suppressing minor infestations of Eastern tent caterpillar. These insecticides are stomach poisons so caterpillars must ingest the material to be negatively affected. When caterpillars are mature and approximately 2 inches long, then pyrethroid-based insecticides, such as bifenthrin, cyfluthrin, and lambda-cyhalothrin should be applied. It is important to apply insecticides when caterpillars are active during the daytime to increase exposure to the insecticide. However, pyrethroid-based insecticides are harmful to pollinators (e.g. honey bees) and beneficial insects. Therefore, do not apply pyrethroid-based insecticides when pollinators are active. For more information on managing Eastern tent caterpillar populations contact your county or state extension specialist.