Malacosoma americanum
eastern tent caterpillar moth

Eastern tent caterpillars, Malacosoma americanum, range throughout the eastern and central United States and are found as far west as the Rocky Mountains. (Wagner, 2005)

Eastern tent caterpillars are often found in forests and near human habitations. Between early spring and early summer, they build silk tents where branches of small trees meet. Preferred species of tree include peach (Prunus persica), cherry and plum (Prunus), hawthorne (Crataegus), and apple and crabapple (Malus domestica). They also build tents in other species of broadleaf trees and shrubs, such as ash (Fraxinus), birch (Betula), willow (Salix), maple (Acer), oak (Quercus), and poplar (Populus). Eastern tent caterpillars are active as moths from late May to June, where they can be found in a variety of habitats including landscaped properties, although they are much more abundant in wooded areas. (Costa, 1998; Drees and Jackman, 1999; Hyche, 1996; Shetlar, 2000; Wagner, 2005)

Adult (moth) Eastern tent caterpillars are reddish brown in color and have two creamy white stripes running obliquely across their front wings. Wingspan is approximately 2.5 cm. Adults have siphoning mouthparts, and females are generally larger than males.

As caterpillars, they can reach 4 to 5 cm in length, and their long setae give them a fuzzy appearance. Color varies, but most are black with a white dorsal stripe and brown and yellow lateral lines. Many also have blue spots along their sides. Caterpillars have chewing mouthparts, used to consume leaves.

Egg masses of Eastern tent caterpillars encircle branches and are covered with shiny, black or dark grey varnish-like material. Tents of Malacoso americanum are among the largest of any tent caterpillar and are typically constructed where two branches meet. Tents usually face southeast. Cocoons are white or yellow. (Drees and Jackman, 1999; Hyche, 1996; Mahr, 2005; Shetlar, 2000; Wagner, 2005)

Eastern tent caterpillars mate soon after emergence. Females attach eggs to branches in masses of about 150 to 400 eggs. Egg masses encircle small branches or twigs and are covered with shiny, black or dark grey varnish-like material. In about 3 weeks, embryos develop to first-stage larvae. Larvae enter diapause and spend summer, fall and most of winter unhatched. Eggs begin to hatch late February and early March, just as leaf development begins to occur. Newly hatched caterpillars feed on the egg mass covering and then move to a nearby fork in the branches where they spin silk to form a tent. Eastern tent caterpillars have 6 larval instars. After 4 to 6 weeks of feeding on leaves, caterpillars reach about 5 cm in length and are fully grown. They then leave the tent and spin a silk cocoon in a protected place such as under rocks, logs, debris on the ground, or cracks of buildings. The pupal stage lasts 3 to 4 weeks. Eastern tent caterpillars live about 5 days as adults. (Choate and Rieske, 2005; Costa, 1998; Fitzgerald, 2007)

Male Eastern tent caterpillars seek females even before females have left the cocoon, flying from cocoon to cocoon waiting for females to emerge. There are generally a higher number of males than females. Mating behavior of both males and females varies with sex ratio and population abundance. Especially when competition is high, males may attempt to mate with females that are already copulating. Increased male competition allows females to select and reject potential mates. Males may or may not hold onto the substrate while mating. Copulation generally ends shortly after a female begins fanning her wings, although if competition is high, males may prolong copulation. Females die soon after breeding. Eastern tent caterpillars are polygynangrous. (Fitzgerald, 2007; Hyche, 1996)

Eastern tent caterpillars breed once a year, mating soon after emergence. After copulation, females lay their eggs in a protected area in masses of 150 to 400 eggs. Eggs are cylindrical and measure about 1 mm in length. Eggs are placed in rows on a twig, and eggs and twig are wrapped with a frothy, shiny material called spumaline. Egg masses of Eastern tent caterpillars are easy to recognize. Eggs hatch during late February and early March, just as leaf development begins to occur. (Hyche, 1996)

Female Eastern tent caterpillars cover egg masses with a protective substance, spumaline. The spumaline coating also serves as the first meal for hatching caterpillars. Because females die soon after breeding, they do not actively provide parental care after eggs are laid. (Hyche, 1996)

Eastern tent caterpillars live about 10 months in total. Adults may live for 5 days. Females usually die soon after laying eggs. (Fitzgerald, 2007; Hyche, 1996)

Eastern tent caterpillars are social, and as caterpillars they live in “cohorts," which are initially formed from sibling groups. Typical sibling group size (third instar) is 50 to 200 individuals. Populations at a given time can contain sub-populations of multiple instar stages.

When not feeding, a cohort of Eastern tent caterpillars aggregates within their silken "tent." The size of the tent increases as the caterpillars grow. Tents are thought to provide shelter from parasites and from some predators as well. They also aid in thermoregulation, and tents often have zones of varying temperature, caused by effects of sun, air currents, and aggregations of caterpillars within it. Individuals within a tent have been observed to move to warmer or cooler sections of the enclosure as need for heating or cooling dictates. In situations of high ambient heat, caterpillars have been observed hanging by their prolegs from the lower surface of the tent.

Eastern tent caterpillars are among the first leaf-eaters to appear in the spring, and their emergence is synchronized with the appearance of early leaves on host trees. They typically remain in the tree on which they emerged as long as sufficient food resources are available. If supply of suitable leaves becomes marginal, or if density becomes very high, caterpillars migrate to other trees.

As Eastern tent caterpillars forage, they leave an "exploratory" trail of silk secreted from spinnerets. When they follow exploratory trails back to their tent, they may overmark the trail, creating "recruitment trails." They leave behind pheromones, deposited by dragging their abdomens, indicating where high quality food has been found. A single individual can even recruit the entire colony to a food source through this method. Movement of Eastern tent caterpillars is largely confined to trails and frequently used trails become conspicuously marked. (Fitzgerald, 2007; Reiske and Townsend, 2005; Wagner, 2005)

Little information is currently available regarding the home range of Eastern tent caterpillars.

Eastern tent caterpillars have a well-developed system for making chemical trails, perceiving trails made by others, and reinforcing trails according to the feeding experience associated with them. An initial "exploratory" trail made by a foraging individual is recognizable by others; if the foraging path proves fruitful, reinforcing pheromones will be added to it by the original forager and subsequent trail followers, thereby recruiting others to benefit from quality food sources (a "recruitment trail"). Individuals choose a trail reinforced by more foragers over one that has had fewer reinforcers.

Caterpillars are also sensitive to light and can perceive images in at least a crude manner. Experimentation has demonstrated capability to perceive a tree-like vertical shape from modest distances as well as capability to discern a difference between objects of different reflectivity. They are also able to sense the direction of the sun. When presented experimentally with an undifferentiated barren field (an extensive asphalt surface), they move in directions that are strongly correlated with sun orientation at the time of the experiment. (Fitzgerald, 2007; Reiske and Townsend, 2005; Wagner, 2005)

Newly hatched Eastern tent caterpillars initially consume the coating that surrounded the egg mass. After constructing a tent, they typically leave the tent prior to dawn, evening and night to feed on leaves. They retreat to the tent between feeding bouts and to avoid midday heat or rain. Eastern tent caterpillars prefer leaves of peach (Prunus persica), plum (Prunus), hawthorne (Crataegus), apple and crabapple (Malus domestica) and cherry trees such as black cherry (Prunus serotina), pin cherry (Prunus pensylvanica), and choke cherry (Prunus virginiana). Their favored host plants are black cherry trees (Prunus serotina). If resources are limited, they may also consume leaves of other species of broadleaf trees and shrubs, such as maple (Acer), and oak (Quercus). Eastern tent caterpillars can quickly damage sections of a tree. Adults do not feed. (Costa, 1998; Drees and Jackman, 1999; Hyche, 1996; Mahr, 2005)

Predation is the most significant cause of mortality in Eastern tent caterpillars. Colonies between the first and second instars are the most preyed upon, and as instar number increases, so does their survival rate. Birds are their most common predators and often destroy the tent and consume the better part of the colony. Avian predators prefer younger larvae and pupae, and final instar caterpillars are rarely attacked, presumably due to setae and toxicity. Eastern tent caterpillars also have a variety of invertebrate predators, although they generally do not destroy the entire colony.

Eastern tent caterpillars are aposematic, resting together in groups on the surface of their tent. They also thrash the anterior part of their body when predators are detected. Other caterpillars in the colony also begin to trash, which deters timid predators such as stink bugs. (Costa, 1998; Fitzgerald, 2007)

Eastern tent caterpillars build their tents on and consume the leaves of a variety of trees and shrubs, particularly members of the family Rosaceae such as apple and crabapple (Malus domestica) and cherry (Prunus). Their favored host plant are black cherry trees (Prunus serotina). They also have a variety of avian and invertebrate predators. Attacks of an avian predators often increase the likelihood of an invertebrate attack due to damages sustained to the tent. Eastern tent caterpillars also host a number of parasites, like Tachinid flies. Eastern tent caterpillars may fall victim to a variety of pathogens, including the viruses Clostridium and Bacillus. Disease mortality does not often parallel predation mortality, but severe outbreaks have been known to occur. (Costa, 1998)

There are no known direct positive effects of Eastern tent caterpillars on humans. As prey for birds and invertebrates, however, they help maintain a forest ecosystem.

A single colony of Eastern tent caterpillars can completely defoliate small ornamental trees, and heavy infestations can cause serious damage to larger trees. Damage to already weakened trees can be fatal. Tents are considered unsightly and are thus removed by land owners. For aesthetic reasons, this species can be considered a pest, particularly to outdoor recreational areas. Eastern tent caterpillars are also serious pests in apple orchards, and many pest-management programs have considerably reduced their presence in orchards. Additionally, Eastern tent caterpillars are associated with Mare Reproductive Loss Syndrome (MRLS). MRLS caused approximately 330 million US dollars in losses in 2001. (Hyche, 1996; Mahr, 2005; Shetlar, 2000; Webb, et al., 2004)

Although pest-management programs are in place in many orchards and sunburn recreational areas, Eastern tent caterpillars are not threatened. This species has not been evaluated by the ICUN or the US Fish & Wildlife Service.