Every ten years or so you might notice an abundance of tent caterpillar nests like the one pictured above. The eastern half of the U.S and Canada get hit hard, but I’m sure our readers along the pacific coast and in the U.K. can relate to this as well.
Eastern tent caterpillars overwinter in a black, styrofoamy egg mass and hatch in the early spring by the hundreds. They build a silky web-like tent in the fork of a tree branch to shelter them at night and during rain. They live as one great big family inside the nest at night.
They leave each day in search of tender spring foliage and use a silk and pheromone trail to find their way back to the web at night.
Apple and cherry trees are a favorite. Around here, it’s pretty common to see long stretches of webs along the wild cherry trees and crab apple trees that line the highway. They don’t seem to like red maples, sycamores, or conifers much.
The Eastern Tent Caterpillar is easily identified outside of its tent by the solid yellow stripe down its back. Their cousins, the Forest Tent Caterpillar look very similar but do not make a webby nest. They like to hang out in large groups and can be identified by the broken, spotty stripe down their backs.
There is also a Western Tent Caterpillar. These fuzzy tent builders have a checkered yellow pattern down their back.
You’ll see tent caterpillars about the time that new spring leaves start to uncurl. They hang around for about 6 weeks, fatten up on leaves then crawl off to find a safe place to spin a cocoon.
Caterpillars will defoliate trees fairly quickly but rarely do any permanent damage. When the tree loses its leaves, its growth might slow a little or it might become slightly less resistant to disease. For an otherwise healthy tree, this won’t be an issue. There is little reason to worry about tent caterpillar control.
As nature would have it, the average tree can tolerate 2-3 consecutive years of defoliation. Tent Caterpillar populations tend to rise for 2-3 years then naturally decline. The caterpillars are native to our area. They are part of our ecosystem and they rise and decline on a ten-year cycle. They are a natural occurrence and for most of us, there is no need for tent caterpillar control…unless you have horses.
In 2001, farms in Kentucky, Ohio, Indiana, and Illinois reported a record number of miscarriages and stillbirths in horses. After ruling out a bunch of factors, it was discovered that the Eastern Tent Caterpillar is linked to Mare Reproductive Loss Syndrome. I’m no veterinarian, but from what I gather when the horses eat the caterpillars the prickly hair stick inside the horse’s digestive track and cause a whole mess of trouble in pregnant mares. Caterpillars sometimes mistake fence posts for tree trunks- making them readily available for snacking.
If you can find the egg mass, removing it before it hatches is a good way to prevent tent caterpillars on your tree. There are sprays available as well. The “old school” way of dealing with tent caterpillars is to burn the nest. This often causes a lot more damage to the tree (and your eyebrows) than the caterpillars would have inflicted.
If you are noticing webs in the late summer or early fall, you are probably seeing webworms. Webworms look similar to tent caterpillars except there are no distinct lines or patterns running down their backs. Their pattern runs along their side.
Fall Webworms build their tent on the tips of a tree branch. (Tent caterpillars build their nests toward the center of the tree in forked branches.) Fall Webworms do not generally leave their tent. The feed inside their tent where they are protected from predators. Once they defoliate one area, they build their tent over another.
As with tent caterpillars, webworm damage is primarily cosmetic. The easiest way to remove a web worm nest, is to clip and dispose of the affected branch. You can also break open the web, making the webworms more accessible to birds or other insects that will eat them.