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How to identify it
- Caterpillars are hairy and black with a white stripe down the back, brown and yellow lines along the sides, and a row of oval blue spots; full-grown they're 2 to 2-1/2 inches long.[1]
- Tents are built in the crotches of limbs and can grow a foot or more long.[1]
- Egg masses of 150 to 400 eggs encircle pencil-thin twigs and are covered with a shiny, black, varnish-like coating.[1]
- Young caterpillars are dark with two thin yellow stripes along the back. Caterpillars of every size are covered in long, pale defensive hairs.[3][4]
- The moth is reddish brown to tan and furry-looking, with two pale stripes running diagonally across each forewing.[1][3][4]
- Cocoons are about 1 inch long, white or yellowish, and spun in dry, sheltered spots on fences and other objects; they are filled with a yellow powder.[1][3][2][4]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Fall webworm | Fall webworm webs are at the ends of branches and enclose the foliage, and they generally appear later in the season.[1] |
| Forest tent caterpillar | Its caterpillars have a row of white keyhole-shaped spots down the back instead of a solid white stripe, and they make only silk mats on trunks and branches, never a tent.[2][3][4] |
| Spongy moth | Spongy moth caterpillars have five pairs of blue dots followed by six pairs of red dots along the back and make no silk webs or tents, though they can be out at the same time as tent caterpillars.[5] |
Where it lives
A native North American insect whose populations rise and fall, with outbreaks every several years; hosts include wild cherry, apple, crabapple, hawthorn, maple, peach, pear and plum.[1]
Biology and life cycle
Caterpillars hatch about when buds open, usually in early March in Kentucky, and stay in the tent during heat or rain, coming out to feed in the morning, evening or at night.[1]
After 4 to 6 weeks they wander off to spin cocoons; reddish-brown moths with two pale diagonal stripes emerge about three weeks later. There is one generation a year.[1]
Parasitic wasps, predators and diseases help keep numbers down in most years.[1]
The tent works mainly as shelter: UMass says it keeps the caterpillars warm on cold spring nights, and Penn State says it protects them from predators and parasitoids.[2][3]
Few birds eat the older, hairy caterpillars. Cherry leaves contain cyanide-producing compounds, and when disturbed the caterpillars can bring up cyanide-laced fluid and thrash as a group to drive off predators.[4][2]
In a study of caterpillars from Washington, D.C., and Georgia, warmer winters made eggs hatch earlier; in the field, hatching came before budburst in both years, and caterpillars that went without food early on died in large numbers.[9]
Damage and signs
- Defoliation and unsightly tents; wandering caterpillars are a nuisance on walks and buildings but do no further feeding damage.[1]
- Because they hatch early, the caterpillars may eat all the new buds and leaves, so a tree can look as if it never leafed out.[3]
- Healthy trees can stand the loss, but repeated heavy defoliation, or another stress such as prolonged drought or disease soon after, can harm a tree, and young, diseased or stressed trees may be killed.[2][4]
Health risk
To people they are mostly a nuisance, but the hairs of some caterpillars can irritate skin, eyes and lungs, and MedlinePlus advises against touching fuzzy or bristly caterpillars. For horses they are a real hazard: pregnant mares that swallow the caterpillars can abort.[6][8][7]
Control
Traps and physical control
In winter, remove and destroy egg masses from ornamental and fruit trees.[1]
In early spring, pull out small tents by hand, or prune out or wind up larger tents on a stick. Don't burn tents with a torch; it damages the tree.[1]
Breaking open tents with a pole can drop the caterpillars to the ground, where predators and parasitoids can reach them, and some land managers break up nests with high-pressure water sprays. Never set fire to tents.[2][3]
Biological control
Bacillus thuringiensis kurstaki kills young caterpillars; insecticides are generally ineffective against mature ones, and caterpillars inside the tent are protected.[1]
Pesticides
Insecticides usually aren't needed. If you spray, do it on warm spring days when the caterpillars are outside the web feeding, since the silk shields them. Penn State lists Bt or horticultural oil for young caterpillars and keeps broad-spectrum products as a last resort.[2][3][1]
Horses and tent caterpillars
In the springs of 2001 and 2002 a wave of abortions in mares, now called mare reproductive loss syndrome, hit the Ohio River Valley. In 2001 about a quarter of pregnant mares there aborted, more than 3,000 pregnancies lost.[8][7]
Feeding trials showed the cause: mares that ate eastern tent caterpillars aborted, while mares fed heat-treated caterpillars, or the caterpillars' droppings, did not. The hairs embed in the gut wall, and the researchers think gut bacteria get into the blood through those wounds and infect the fetus.[7][8]
The only known prevention is keeping horses, especially pregnant mares, away from eastern tent caterpillars and probably most other hairy caterpillars.[8]
If caterpillar hairs get on your skin
MedlinePlus says most caterpillars are harmless, but some hairs cause allergic reactions in the skin, eyes or lungs. Lift hairs off skin with sticky tape, repeating until they are gone, then wash with soap and water. If hairs get in your eyes, flush them with plenty of water and get medical help, and get medical care if hairs are breathed in.[6]
Where sources disagree
Hatch time: Kentucky says caterpillars usually hatch in early March, the Missouri Department of Conservation shows young tents by mid-March, and UMass says they hatch in April.[1][4][2]
Size and egg count: Kentucky gives full-grown caterpillars as 2 to 2 1/2 inches and egg masses of 150 to 400 eggs, while UMass gives 1 1/2 to 2 inches and 150 to 350 eggs, and Penn State about 2 inches and 150 to 350 eggs.[1][2][3]
Outbreaks: Kentucky says outbreaks come every several years, while UMass and Penn State put them at eight to 10 year intervals.[1][2][3]
Moth flight: the Missouri Department of Conservation says adults fly in May and June, while UMass and Penn State say they emerge in late June and July.[4][2][3]
Common questions
- Will tent caterpillars kill my tree?
- Usually not. Even heavily defoliated trees typically recover and put out a new crop of leaves.[1]
- Are tent caterpillars dangerous to horses?
- Yes, to pregnant mares. Eating the caterpillars can cause mare reproductive loss syndrome, a form of abortion, so keep mares away from them.[8][7]
- Should I burn the tents?
- No. Kentucky, UMass and Penn State all warn that burning tents damages the tree more than the caterpillars do. Pull out small tents, or wind larger ones onto a stick.[1][2][3]
Sources
- University of Kentucky Entomology, “ENTFACT-423: Eastern Tent Caterpillar (revised January 2026).” entomology.mgcafe.uky.edu/ef423 (accessed 2026-11-11)
- UMass Extension Landscape, Nursery and Urban Forestry Program, “Eastern Tent Caterpillar (Landscape fact sheet).” ag.umass.edu/landscape/fact-sheets/eastern-tent-caterpillar (accessed 2026-11-11)
- Penn State Extension, “Eastern Tent Caterpillar.” extension.psu.edu/eastern-tent-caterpillar (accessed 2026-11-11)
- Missouri Department of Conservation, “Eastern Tent Caterpillar Moth (Field Guide).” mdc.mo.gov/discover-nature/field-guide/eastern-tent-caterpillar-moth (accessed 2026-11-11)
- UMass Extension Landscape, Nursery and Urban Forestry Program, “Spongy Moth (Landscape fact sheet).” ag.umass.edu/landscape/fact-sheets/spongy-moth (accessed 2026-11-11)
- MedlinePlus, U.S. National Library of Medicine, “Caterpillars (Medical Encyclopedia).” medlineplus.gov/ency/article/002860.htm (accessed 2026-11-11)
- Journal of Insect Physiology, via PubMed, “Eastern tent caterpillars (Malacosoma americanum) cause mare reproductive loss syndrome (Webb et al. 2004).” pubmed.ncbi.nlm.nih.gov/15019520/ (accessed 2026-11-11)
- Journal of Animal Science, via PubMed, “Invited review: the role of caterpillars in mare reproductive loss syndrome (McDowell et al. 2010).” pubmed.ncbi.nlm.nih.gov/20081071/ (accessed 2026-11-11)
- Oecologia, via PubMed, “Warming affects hatching time and early season survival of eastern tent caterpillars (Abarca and Lill 2015).” pubmed.ncbi.nlm.nih.gov/26093630/ (accessed 2026-11-11)
- iNaturalist, “Malacosoma americana taxon page (order and family).” www.inaturalist.org/taxa/211100 (accessed 2026-11-11)