Ask a Master Gardener
Eastern Tent Caterpillars
I am seeing webs of some kind of insect in my tree where the branches join. What are these and what should I do about them? EC
It sounds like you are describing Eastern Tent Caterpillars. These insects are similar to the Fall Web Worms we see each fall, but they manifest differently.
One of the main differences you will notice is the webbing. Eastern Tent Caterpillars tend to build their webs where the branches split off the main stem while Fall Web Worms build their webs out at the end of the branches. Knowing this alone will help you distinguish between the two. And Eastern Ten Caterpillars are out and about in the spring while Fall Web Worms are more visible in the fall.
These caterpillars grow to be about 1 to 1.5 inches in length and have light colored keyhole shaped marking down their back. The caterpillars we are seeing now have overwintered in protective egg mass. These egg masses are kind of a dark hard mass that encircles a twig and kind of look like they were enameled. There can be 150 to 350 eggs in each of these egg masses. They hatch and begin to feed in mid-February to mid-March. As they eat and grow their webs will expand in size.
The Eastern Tent Caterpillar feeding frenzy lasts about six to eight weeks. They then migrate to a protected area to spin their cocoons and enter the pupal stage which lasts about three weeks. They emerge in late June and July as moths and the females deposit their eggs on branches like before. These moths only live for a few days.
Easter Tent Caterpillars tend to prefer cherry, crabapple, and apple trees but may dine on other deciduous ornamental shrubs and trees.
These caterpillars do not feed inside the web but gather together there during the night and inclement weather. When they have sufficient numbers, they can defoliate a tree but seldom kill the tree. These caterpillars are also a food source for other insects, toads, and birds.
The best way to control these insects is to look for the egg masses. If you find one, just clip off that branch and your work is done. If you have an Eastern Tent Caterpillar web, you can just break apart the webbing and dispose of what you can remove. This will also help expose the caterpillars to birds who have a hard time reaching them inside their webs.
An organic pesticide such as bacillus thuringiensis can be sprayed in the area surrounding the web so that when they emerge to feed, they will eat the leaves covered with the pesticide and die. Unfortunately, it is difficult for homeowner to spray appropriately when the infestation is high in a tree.
Ultimately, if you have Eastern Tent Caterpillars, you may want to just live and let live. Their webs can be unsightly and their migrations to pupate a little un-nerving, but ultimately, they tend not to do fatal damage to the tree.
You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at firstname.lastname@example.org.
Photo: William H. Hoffard, USDA Forest Service, Bugwood.org