Families: Erebidae, Lasiocampidae
Tent caterpillars, Malacosoma spp.
The forest tent caterpillar (Malacosoma disstria) is commonly found in urban areas and is the most damaging of the tent-making caterpillars. Rather than constructing tents, forest tent caterpillars deposit silken mats on trunks and large branches which they use for molting and resting between feeding periods. Their larvae are dark-gray to brownish-black with thick pale-blue lines and small, broken yellow lines along each side.
Fully grown caterpillars of the forest tent caterpillar (Malacosoma disstria), eastern tent caterpillar (Malacosoma americanum), and western tent caterpillar (Malacosoma californicum) are roughly 50 mm (2 inches) in length.
Adults are generally a yellowish-brown color with faint wavy bands on the wings. These moths have a wingspan of 25–75 mm (1-3 inches). Many Malacosoma spp. are hairy with feathery antennae.
Fall webworm, Hyphantria cunea
Fully mature larvae have hairy lime green bodies with dark spots and a black or red head capsule. Mature caterpillars can reach up to 25 mm (1 inch) in length.
Fall webworm moths are bright white and hairy, with bright yellow to orange front legs. These moths have a wingspan of 35–42 mm (1.4-1.7 inches).
Tiger moth, Lophocampa spp.
The caterpillars of tiger moth species typically have furry bodies and reach a length of about 37 mm (1.5 inches).
Tiger moths typically have dark wings with white stripes and sometimes orange or red spots. In some species these colors are arranged in aesthetically pleasing geometric patterns. Moth size depends on species; southwest pine tiger moth (Lophocampa ingens) adults have a wingspan of about 40mm (just over 1.5). Silver-spotted tiger moth (Lophocampa argentata) adults are larger with a wingspan of about 50 mm (2 inches).
• There are several species of tent-making caterpillars in Colorado; all are moths.
• Different species tend to create tents throughout the season. For example, tent caterpillar (Malacosoma spp.) and tiger moth (Lophocampa spp.) outbreaks occur in early spring, while fall webworm (Hyphantria cunea) tents can be found on cottonwood, chokecherry, and other trees during the summer.
• Stressed plants with early season defoliation are most susceptible to injury. Although their tents can be large and unattractive, these caterpillars rarely cause significant injury to healthy plants.
Early instar larvae of the Eastern tent caterpillar. Tent-making caterpillars are the larvae of several moth species. While their tents may be unsightly, these caterpillars do not usually cause serious harm to the host plant. Image credit:Tim Tigner, Virginia Department of Forestry, Bugwood.org
Fall webworm tent on hickory. Image credit: Penn State Department of Plant Pathology & Environmental Microbiology Archives., Penn State University, Bugwood.org
Tiger moth colony of mature caterpillars. Image credit: William M. Ciesla, Forest Health Management International, Bugwood.org
Fall webworm adult. Image credit: Jerry A. Payne, USDA Agricultural Research Service, Bugwood.org
Complete defoliation caused by eastern tent caterpillar. Image credit: Robert L. Anderson, USDA Forest Service, Bugwood.org
Life history and habits
Tent caterpillars overwinter in egg masses on the twigs of a suitable host plant. Soon after budbreak, caterpillars emerge and begin producing silken tents, which provide shelter for the developing insects. Tent caterpillars tend to leave the silk shelter to feed at night and return by daylight. However, sometimes they will also feed during the day. As caterpillars grow, the tent is enlarged to accommodate their increasing size; by late spring caterpillars are fully grown. Most caterpillars leave the tent and pupate in a white cocoon. Adult moths emerge about two weeks later. There is a single generation a year.
Fall webworm overwinters as a pupa, buried loosely beneath debris near previously infested trees. Adults emerge in June and July. After mating, pregnant females lay egg masses on the leaves of trees and shrubs. Eggs hatch soon after they are laid, and the newly emerged caterpillars cover only a few leaves as they feed and grow. Silk coverage on the plant increases as the caterpillars grow, and the caterpillars tend to feed within the tent. Fully grown caterpillars leave the tent and can become a nuisance around households as they crawl on fences and walls.
Tiger moth caterpillars continue feeding and developing through the winter. Tents are produced in early spring on terminal growths of ponderosa pine, lodgepole pine, pinyon, Douglas-fir, white fir, and juniper. Development is completed by June and the caterpillars begin to pupate. By August, adult moths have emerged and begin to lay egg masses. The eggs hatch before fall.
Control is only warranted when high levels of defoliation are sustained over several years.
Tents can be physically removed from the tree if accessible. Pruning and burning cause more injury to the plant and are not recommended.
Birds, predatory insects, and parasitic wasps are natural enemies of tent making caterpillars. There are also microbial pathogens, e.g., viruses that help decrease caterpillar populations. For this reason, serious outbreaks do not usually last longer than one season. However, in some areas fall webworm is an annual problem.
Microbial insecticides containing Bacillus thuringiensis (Bt) can be effective in controlling tent making caterpillars. However, Bt is only effective when consumed by caterpillars and should be applied to leaves before they are covered with silk.
Contact insecticides can be effective management options for these caterpillars. Various pyrethroid containing insecticides are available for homeowners, as are some carbaryl containing insecticides. Consult the full factsheet for more information.
Bugguide.net. 2022. Species Lophocampa argentata – Silver-spotted Tiger Moth. Available https://bugguide.net/node/view/43315
Ciesla, W. & Ragenovich, I. (n.d.). Western tent caterpillar. US Department of Agriculture: Forest Service – Forest Insect & Disease Leaflet 119. Available https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev2_042847.pdf
Encyclopedia Britannica. (n.d.). Tent caterpillar moth. Encyclopedia Britannica. Available https://www.britannica.com/animal/tent-caterpillar-moth
Encyclopedia Britannica. (n.d.). Tiger moth. Encyclopedia Britannica. Available https://www.britannica.com/animal/tiger-moth
University of Florida. 2021. Featured Creatures: Fall Webworm. University of Florida Institute of Food and Agriculture. Available https://entnemdept.ufl.edu/creatures/trees/moths/fall_webworm.htm#:~:text=A%20fall%20webworm%20tent%20normally,reach%20one%20inch%20in%20length.