Tent caterpillars are very social insects. They hatch together; they build a home together; they eat together, and they defend themselves against predators together. A single group of tent caterpillars may include up to 300 individuals. Tent caterpillars are easily recognized because they are colorful and active during the day. When they are not eating or traveling together, they like to bask in the sun together.
Tent caterpillars are the larvae of moths. They are called tent caterpillars because they make webbed tents in the forks and crotches of trees. They are often found in apple, pear, peach, cherry, and other fruit trees. Some species of tent caterpillar, such as the eastern tent caterpillar, build one large tent for the group. Other species build a series of small tents.
Tent caterpillars hatch from their eggs in early spring at about the time the leaves of their host trees are just unfolding. Soon after hatching, the caterpillars band together to establish their tent. They always choose a spot that is warmed by the early morning sun. They choose a sunny spot because body warmth is important for their digestion of food. It is important that they elevate their body temperature above the temperature of their immediate surroundings.
Tent caterpillars spin silk to create their tent. Caterpillars make silk from modified salivary glands their lower lip. The silk is emitted from a tube on the lip and dries immediately upon contact with air. A tent usually contains several separate compartments or layers. Tent caterpillars will move from compartment to compartment during the day. They can adjust their body temperature by moving from one compartment to another. At the start of cool days, for example, they will huddle in a compartment facing the morning then move together from compartment to compartment following the movement of the warming sun. When it’s chilly, tent caterpillars nestle together to share their body warmth. The temperature of a tent caterpillar group under the sunlit surface of the tent can be as much as 54 °F (30 °C) warmer than the surrounding air temperature. When daytime temperatures rise later in spring, tent caterpillars may retreat to the shaded outside surface of the tent to cool down.
When tent caterpillars are hungry, they often set out together to find leaves to feed on. Lead caterpillars will lay down pheromone trails for other caterpillars to follow. This is similar to the chemical trails used by ants and termites. If birds or other predators disturb them, tent caterpillars will rear up together and thrash back in forth in unison. Because their bodies are covered in bristles that can irritate predators. Tent caterpillars are often considered pests due to their ability as a group to defoliate a tree.
Tent caterpillars grow rapidly. They complete their larval development in seven to eight weeks. When fully grown, the tent caterpillar will find a protected spot on the ground or in a tree to spin its cocoon. About two weeks later, it emerges as an adult moth. An adult moth may live its entire life in a week or less. During that time adults will mate and the female moth will lay a mass of 150 to 400 eggs on a tree branch. There is usually one brood per year. The insects will pass the winter in the egg stage before emerging the next spring. Caterpillars from one egg mass will stay together to build the next tent.
There are 26 species of tent caterpillars. Perhaps the two best known are the eastern tent caterpillar and the forest tent caterpillar. The eastern tent caterpillar is found in the eastern and central United States. The larvae are black with a white stripe down the back, brown and yellow lines along the sides, and a row of oval blue spots on the sides. They are 2 inches (5 cm) long when fully grown. The forest tent caterpillar is found throughout North America. Other species are found in Eurasia. The scientific name of the eastern tent caterpillar is Malacosoma americanum. The scientific name of the forest tent caterpillar is Malacosoma disstria.
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