Malacosoma

Larvae are distinguished from other caterpillars by their construction of large, communal silken tents in the crotches of branches, which they enlarge as they grow. The combination of hairy bodies, bold striping patterns, and trail-following behavior along silk highways separates them from solitary caterpillar species. Adults are less frequently observed but can be recognized by their robust, furry bodies and association with known larval host trees.

Adults are medium-sized moths with stout, furry bodies. Larvae are hairy caterpillars with distinctive color patterns; for example, Malacosoma americanum has blue stripes and patches on the sides with a white stripe down the center of the back. Larvae possess a posterior gland that deposits trail-marking pheromones. Egg masses are dark brown, Styrofoam-like, and encircle small branches.

Forest and woodland ecosystems, including deciduous forests, orchards, and riparian corridors. Some species occupy arid regions; for example, Malacosoma californicum occurs in the Mojave Desert on desert almond (Prunus fasciculata). Larvae require woody host plants for feeding and tent construction.

Holarctic distribution spanning the Nearctic and Palearctic regions. Malacosoma americanum occurs in eastern North America from Canada to the southeastern United States. Malacosoma californicum ranges across western North America from Alberta to California and Arizona. Malacosoma disstria is widespread across North America. Palearctic species include M. neustria and M. castrense in Europe and Asia.

Larvae are active in spring, typically emerging with the bloom of forsythia in eastern North America. Activity occurs primarily March through April, with adult moths emerging in June or July. Populations exhibit cyclic outbreaks with multi-year periodicity.

Larvae feed on foliage of woody plants. Oligophagous species such as Malacosoma americanum feed primarily on Rosaceae including cherry (Prunus), apple (Malus), and crab apple. Polyphagous species such as Malacosoma disstria and M. californicum consume a broader range including alder, oak, poplar, and willow in addition to Rosaceae.

• Prunus serotina - hostPreferred host of M. americanum
• Prunus pennsylvanica - hostWild cherry host
• Prunus virginiana - hostWild cherry host
• Malus coronaria - hostWild apple host
• Malus domestica - hostCultivated apple
• Prunus fasciculata - hostDesert almond; host of M. californicum in Mojave Desert

Winter is spent as eggs in dark, foam-like masses encircling small branches. More than 300 larvae may hatch from a single egg mass in spring. Larvae construct silken tents over the egg mass and surrounding branch, expanding and relocating tents to branch crotches as they grow. Development occurs through spring, followed by a mass exodus from host trees. Larvae wander to protected locations beneath logs, leaves, stones, or structures to spin yellowish-white silken cocoons. Adults emerge from cocoons in June or July, mate, and females deposit eggs on small branches of host trees.

Larvae exhibit highly social behavior with communal foraging, tent construction, and maintenance. Siblings from the same egg mass cooperate in enlarging tents and locating food. Trail-marking pheromones deposited by the posterior gland allow caterpillars to recruit nestmates to food sources. Tents serve thermoregulatory functions, elevating body temperature for faster growth on cool days, and provide protection from predators and parasites. Late-instar larvae disperse individually to pupation sites.

Significant defoliators of deciduous trees and shrubs, capable of stripping foliage from small and large trees during outbreak years. Serve as hosts for parasitoids including the tachinid fly Leschenaultia exul. Population cycles are regulated by natural enemies including predators, parasites, and pathogens. Defoliation may reduce tree vigor, though trees often recover with secondary leaf flush.

Several species are important forestry and orchard pests. Malacosoma americanum is associated with mare reproductive loss syndrome (MRLS) in horses; pregnant mares consuming caterpillars or their setae may abort foals due to bacterial infection introduced by penetrating hairs. Management includes mechanical removal of egg masses and tents, pruning infested branches, and professional arborist intervention for tall trees. Burning tents is not recommended due to bark damage.

• LasiocampaRelated genus in Lasiocampidae; larvae lack communal tent-building behavior and are solitary rather than social.
• EriogasterEuropean lasiocampid with tent-building larvae; distinguished by geographic range and host plant associations.

• forest pest
• defoliator
• social insect
• chemical communication
• thermoregulation

• BugGuide
• Wikipedia
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Get them when they're little - Eastern tent caterpillar, Malacosoma americanum — Bug of the Week
• Hairy wanderers - Eastern tent caterpillars, Malacosoma americanum — Bug of the Week
• Time for tents - Eastern tent caterpillar, Malacosoma americanum — Bug of the Week
• Return of the tent makers - Eastern tent caterpillar, Malacosoma americanum — Bug of the Week
• Tents in the Mojave: Western tent caterpillar, Malacosoma californicum — Bug of the Week
• The silk trail - Eastern tent caterpillar, Malacosoma americanum — Bug of the Week
• Malacosoma americanum . [Distribution map].
• The Biology of Leschenaultia Exul Townsend, a Tachinid Parasite of Malacosoma Americana Fabricius and Malacosoma Disstria Hubner1
• Figure 1: Distributions, sampling locations, and Bayesian cluster membership for three Malacosoma species.
• THE EFFECT OF VARIATION IN HOST PLANT ON THE GROWTH OF AN OLIGOPHAGOUS INSECT, MALACOSOMA AMERICANUM AND ITS POLYPHAGOUS RELATIVE, MALACOSOMA DISSTRIA
• Malacosoma parallelum . [Distribution map].
• Temperature-Dependent and Semi-Quantitative Enzyme Profiles of Malacosoma disstria (Lepidoptera: Lasiocampidae) Hemocytic Cell Lines.