Tent caterpillars
Order: Lepidoptera
Families: Erebidae, Lasiocampidae
Description and life history
Tent caterpillars, Malacosoma spp.
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. 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.
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. Adult moths emerge about two weeks later. There is a single generation a year.
Fall webworm, Hyphantria cunea
Fall webworm moths are bright white and hairy, with bright yellow to orange front legs, with different color forms occurring throughout their range. These moths have a wingspan of about 30 mm (1.1 inches). Newly emerged larvae are pale yellow or yellow-green and have two rows of dark tubercles running along the back, and mature larvae have hairy yellow or green bodies. Populations of fall webworm in the northern range usually produce pure white adults and larvae with a black head capsule, while moths inhabiting the southern range produce adults that have dark spots on wings and larvae with a red head capsule. Mature caterpillars can reach up to 25 mm (1 inch) in length.
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. Tents constructed by fall webworm often enclose branch ends, unlike other tent-making caterpillars whose tents enclose the branch crotches. The webs produced by black-headed larvae tend to be thin and more prone to breakage, while tents produced by red-headed larvae are larger and denser. The web provides protection from predators and provides shelter from unfavorable weather conditions. When disturbed, larvae can often be observed twitching rhythmically within their tents. Most mature caterpillars leave the tent and migrate to bark crevices, under stones, or beneath substrates on soil surface to pupate in a white cocoon These fully grown caterpillars can become a nuisance around households when they crawl on fences and walls.
Tiger moth, Lophocampa spp.
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). The caterpillars of tiger moth species typically have furry bodies and reach a length of about 37 mm (1.5 inches).
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.
Quick Facts
• 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
Injury
Tent caterpillars
Outbreaks of tent caterpillars can result in severe defoliation over large areas, which reduces host growth and productivity. While host mortality is usually low, observations in northeastern Ontario suggest that multiple years of complete defoliation can kill 100% of certain host species, such as trembling aspen (Populus tremuloides). The decline of sugar maple (Acer saccharum) populations in the northeastern United States and Canada has been attributed to tent caterpillar outbreaks. Trees that survive outbreaks can compensate with new growth, although outbreaks of tent caterpillars can significantly alter forest composition and ecosystem dynamics.
Fall webworm
Fall webworm can cause significant cosmetic injury to ornamental trees and orchards. Severe feeding injury can result in the skeletonization of leaves on susceptible hosts. The conspicuous tents are often filled with fecal pellets and larval skins.
Tiger moth
Larvae can defoliate trees and create webs on the upper branches and treetops. Outbreaks are infrequent, and this insect typically causes only minor defoliation. Younger pines appear to be more susceptible to defoliation due to tiger moth feeding, but this is less likely to occur in landscape settings in comparison to natural forests. Trees are usually able to recover from feeding of tiger moth caterpillars without sustaining any lasting injury.
Monitoring
Tent caterpillars can be monitored with traps baited with a sex pheromone. These traps will capture adult males and can be useful in predicting outbreaks.
Cultural control
Cultural control of tent caterpillars can be accomplished through proper watering, which promotes tree health. Egg masses and groups of young larvae on branches or trunks of young trees can be removed and destroyed. Egg masses are easier to find in the winter when leaves are absent. Outdoor lighting can be minimized to reduce attractiveness of the area to reproducing adults. Larvae and pupae can be removed from walls and outdoor furniture with pressurized water or a stiff broom. Tents can be physically removed from the tree if accessible. Pruning and burning cause more injury to the plant and are not recommended.
Fall webworm tents tend to be confined to certain branches, which allows for pruning and destruction of colonies on shorter trees. Removing leaves with egg masses on lower limbs is recommended prior to the emergence of larvae. Creating openings in webs can improve predator and parasite accessibility to the larvae within. However, this approach can leave undesirable gaps in ornamental trees. The use of pheromones in mating disruption or mass trapping can be effective in small, isolated areas where moths are unlikely to be attracted from surrounding areas.
Biological control
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.
Applications of Bacillus thuringiensis (Bt), spinosads, and baculovirus can be effective in controlling tent making caterpillars. Applications of Bt, spinosads, and the nucleopolyhedrovirus (NPV) have minimal impact on nontarget organisms. Bacillus thuringiensis is only effective when consumed by caterpillars and should be applied to leaves before they are covered with silk. However, the efficacy of Bt against tent caterpillars appears to vary among different tree species. The nucleopolyhedrovirus (NPV) has been documented in naturally occurring populations of tent caterpillar in the United States. This virus is most lethal toward young larvae, and while field applications of NPV have significantly reduced the number of tent caterpillar larvae in India, it is unclear how effectively this virus can be used to combat outbreaks in the United States, and which isolates of NPV are likely provide the most control.
Chemical control
Chemical control should be considered only when high levels of defoliation are sustained over several years, and are rarely necessary against tiger moths, who usually remain at low levels and experience infrequent outbreaks. Tent caterpillar infestations can be treated with azadirachtin, insecticidal soaps, or conventional insecticides such as pyrethroids, organophosphates, and carbamates. Chemical control of fall webworm can be accomplished with nonsystemic carbamates, insect growth regulators, and systemic emamectin benzoate. The use of insect growth regulators should be avoided near aquatic habitats to protect aquatic arthropods. Applications for controlling fall webworm are recommended when colonies of small larvae are first observed, and insecticide applications for managing the pecan nut casebearer (Acrobasis nuxvorella) and hickory shuckworm (Cydia caryana), are also effective against fall webworm. Spot treatments of insecticides can be applied to foliage surrounding a web and the web itself can be soaked with the insecticide. Applying systemic insecticides as directed will help limit negative effects on nontarget organisms, such as pollinators.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
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
Gani, M., R. Gupta, V. Kaul, S. Zargar, K. Bali, and G. Khan. 2016. Management Of The Tent Caterpillar (Malacosoma indicum) Using Nucleopolyhedrovirus In Jammu & Kashmir, India. Materials Today: Proceedings. 3(10):3914-3924. Available https://www.sciencedirect.com/science/article/pii/S2214785316304242
Schowalter, T. 2017. Biology and Management of the Forest Tent Caterpillar (Lepidoptera: Lasiocampidae). Journal of Integrated Pest Management. 8(1):1-10. Available https://colostate.primo.exlibrisgroup.com/discovery/fulldisplay?docid=cdi_crossref_primary_10_1093_jipm_pmx022&context=PC&vid=01COLSU_INST:01COLSU&lang=en&search_scope=MyCampus_FC_CI_PU_P&adaptor=Primo%20Central&tab=Everything&query=any,contains,tent%20caterpillar%20management
Showalter, T., and D. Ring. 2017. Biology and Management of the Fall Webworm, Hyphantria cunea (Lepidoptera: Erebidae). Journal of Integrated Pest Management. 8(1): 1-6. Available https://colostate.primo.exlibrisgroup.com/discovery/fulldisplay?docid=cdi_oup_primary_10_1093_jipm_pmw019&context=PC&vid=01COLSU_INST:01COLSU&lang=en&search_scope=MyCampus_FC_CI_PU_P&adaptor=Primo%20Central&tab=Everything&query=any,contains,Fall%20webworm%20management
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.
University of Florida. 2020. Featured Creatures: Forest tent caterpillar. University of Florida Institute of Food and Agriculture. Available https://entnemdept.ufl.edu/creatures/trees/forest_tent_caterpillar.htm#:~:text=Description%20(Back%20to%20Top),keyhole%20or%20shoeprint%2Dshaped%20marking.
US Department of Agriculture. 2011. Forest Tent Caterpillar: Aspen defoliator makes no tent. US Department of Agriculture: Forest Health Protection. Available https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5343832.pdf
Worldspecies.org. 2022. Lophocampa ingens. Worldspecies.org. Available https://worldspecies.org/ntaxa/1500493