By Pamm Cooper, UConn Home & Garden Education Center
Eastern tent caterpillars, Malacosoma Americanum, are native to North America and are noticed mainly because of the silken tents they build in the forks and crotches of trees in early spring. While most tents are found on black cherries, they can also be found on other trees such as apple and crabapple. They are readily visible since tents are constructed before leaves fully expand. There is only one generation per year.
These caterpillars are hairy and dark when small, and later instars have two yellow lines along the back. A white medial stripe goes along the sides of the body, and this is flanked by two yellow lines. There are blue blotches along its side as well. Bottom hairs on the body are rusty brown. Forest tent caterpillars are also hairy, but they do not make tents, and their bodies
are blue with white dots on the back. Handling should be done with gloves on as some people may have sensitivity to the hairs.
Egg masses are black, laid on small branches of host trees the previous year, and the egg mass rings around the branch. Sometimes they are mistaken for small black knot galls. 150-300 eggs may be in each egg mass. Caterpillars typically hatch as black cherry leaves begin to expand the next spring. Caterpillars feed on leaves and buds and rest communally by day in the nests they construct from silk.
While they can almost defoliate small trees, these caterpillars usually have completed their feeding stage in time for the trees to put out new leaves by early summer. The more tents there are on small trees, though, the greater number of caterpillars there are, so damage will increase.
While protected from many predators while inside the tents, there are birds that will tear the tents apart to feed on the caterpillars inside. Both the black-billed and the yellow-billed cuckoos are known for their ability to do this, and native vireos will also seek out and rip apart the tents.
Mature caterpillars leave the host plants in early summer in search of suitable sites to pupate within a silken cocoon they will spin. Moths emerge later that year. The moths have a fluffy light brown body, and the wings have three bands with the center being narrower than the outer bands and a lighter brown in color. The center band is bordered on both sides by thin, creamy bands.
Occasionally, eastern tent caterpillars have outbreak years where large numbers of the tents can be seen on the same tree. Fresh buds may also be consumed if trees are severely defoliated. When found on residential properties, tents can be swept apart by rakes or brooms, exposing caterpillars to predators, or knocking them off the trees. If warranted, foliage can be sprayed with a biological product called Bacillis thuringiensis subspecies, Kurstaki, or BtK, which only harms caterpillars and not other insects. Caterpillars will ingest the product as they feed on the foliage.
Most healthy trees can tolerate severe defoliation from eastern tent caterpillars. If concerned, look for egg masses in the winter on trees that had been damaged the previous spring. Remove them, if possible, or crush them, or prune the branch off below where the egg mass is found. Or let them be if the trees appear to have recovered. Letting nature take its course with native insects on native trees can often benefit birds and other predators. Do not confuse them with the notorious gypsy moth caterpillars which do not make silken tents or nests of any kind.
If you have a question about tent caterpillars or other gardening topics, contact the UConn Home & Garden Education at (877) 486-6271 or www.homegarden.cahnr,uconn.edu or your local Cooperative Extension Center.
