tent caterpillar, common name for the larvae of the members of a family of moths (Lasiocampidae), easily recognized by the large silk tents, or webs, that the larvae construct during the spring in the crotches of trees, particularly apple and cherry trees. Tent caterpillars are hairy and usually brightly colored, with blue and yellow spots. Periodically they become serious orchard pests and occur in large enough numbers to defoliate whole trees and damage the fruit. Many larvae live gregariously within the tent, which they use for shelter during the night and in rainy weather. During the day, the larvae leave the tent and feed on the leaves in nearby branches.

The best-known tent maker is the Eastern tent caterpillar, Malacosoma americanum. In addition to being an orchard pest, it has been linked to mare reproductive loss syndrome (MRLS), in which apparently healthy mares experience high rates (more than 70% in experimental studies) of aborted fetuses or stillborn foals. An outbreak of MRLS resulted in the lost of more than 5,000 foals in Kentucky in 2001. Elimination of caterpillar populations, by removing host trees or eradicating the caterpillars, or otherwise avoiding horse contact with the caterpillars and their waste appears to prevent the syndrome. Other species of Malacosoma occur both in E and W North America and have been known to defoliate large areas by attacking a variety of forest and shade trees. Not all species build tents; despite the name forest tent caterpillar, M. disstria, at times an extremely destructive pest that migrates by the millions to new food plants, never weaves a tent.

The tent caterpillar pupates within the oval white cocoon it spins, and the adult emerges during midsummer as a reddish brown or gray, medium-sized, stout-bodied, hairy moth with feathery antennae. After mating, the adult deposits several hundred eggs, covered by a thick, foamy brown crust, in bands around the twigs of the host tree. The eggs overwinter until the early spring when they hatch. Larvae from several egg masses congregate near a fork in a limb and form the tent by crawling about, leaving silk behind. Removing egg masses during the winter or removing tents in the early spring and soaking them in kerosene or burning them, are the most effective means of control.

Tent caterpillars are classified in the phylum Arthropoda, class Insecta, order Lepidoptera, superfamily Bombycoidea, family Lasiocampidae.

caterpillar, common name for the larva of a moth or butterfly. Caterpillars have distinct heads and are segmented and wormlike. They have three pairs of short, jointed legs (retained in the adult) on the thorax; in addition, they have unjointed, fleshy appendages, called prolegs, on some abdominal segments. The prolegs end in clusters of tiny hooks. There is a row of simple eyes on either side of the body. Sawfly larvae are often mistaken for caterpillars, but their prolegs have no hooks and they have a single simple eye on each side. Almost all caterpillars are vegetarian and have strong jaws for chewing. The chewing mouth parts and the prolegs disappear during the pupa stage, as the larva is transformed into an adult. Caterpillars have silk glands that open into a mouth part called the spinneret. The caterpillar exudes a silk strand continuously as it moves along; small caterpillars swing by the strand when dropping from a height. Many caterpillars use the thread to build a cocoon in which to pupate. Most molt their skin (to accommodate growth) five or six times before pupation. Some caterpillars have smooth skin; others are hairy, such as the woolly bear, or hedgehog, caterpillar of the Isabella tiger moth. The caterpillars of the larger night-flying moths (e.g., the luna moth and polyphemus moth) are smooth and green and may be over 3 in. (7.5 cm) long. Caterpillars are equipped with various protective devices. The io moth caterpillar has sharp spines connected with glands that secrete an irritating substance. Others have irritating bristles, and the swallowtail butterfly larva emits a repellent odor when disturbed. Nevertheless, caterpillars form the major part of the diet of many birds and other animals. Caterpillars are voracious eaters and some cause considerable economic damage. Among these are the appleworm, the cutworm, and the larvae of the bee moth, the codling moth, and the clothes moth. Some moths and butterflies remain caterpillars for two or three months, others for about 10 months, hibernating through the winter in this stage. In the Arctic are some forms that require two or three years to develop from egg to adult.

alfalfa caterpillar, larva of the alfalfa butterfly, Colias eurytheme, a member of the family Pieridae. Found throughout most of Mexico, the United States, and S Canada, it is sometimes a serious pest of alfalfa, clover, and other legumes in the SE United States. It usually overwinters as a pupa, the orange adult emerging in early spring, when large numbers of these butterflies may be seen fluttering low over alfalfa fields. The female lays several hundred eggs on the undersides of leaves. The larvae are fully grown in 12 to 15 days; there are two generations each season in the northern part of the range and up to seven in the south. Low cutting of infested alfalfa, which exposes the larvae to sun and predators, aids control. The alfalfa caterpillar is classified in the phylum Arthropoda, class Insecta, order Lepidoptera, family Pieridae.

Any moth larva of the genus Malacosoma (family Lasiocampidae). Tent caterpillars are often brightly coloured. Congregations of the eastern tent caterpillar (M. americanum) of eastern North America spin huge, tent-shaped communal nests in forked tree branches. Eggs the moth deposits on a tree in midsummer hatch in spring. The hatched caterpillars migrate to a tree crotch and construct a silken tent, which they leave each day throughout the summer to feed on the surrounding leaves. The forest tent caterpillar (M. disstria) is common in the southern U.S.

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Larva of a butterfly or moth. Caterpillars have a cylindrical body consisting of 13 segments, with three pairs of legs on the thorax and “prolegs” on the abdomen. The head has six eyes on each side, short antennae, and strong jaws. Though not true worms, many caterpillars are called worms (e.g., the inchworm, or looper, and the cutworm). Caterpillar-like larvae are also found in other insect groups (e.g., sawflies and scorpionflies).

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