Fall Web Worm

Photo K. Fosty

The fall web worm is a gregarious fellow who likes to get together with friends and eat your prized fruit tree or ornamental. Fall is the time of year when these caterpillars pitch their tents and throw a feast! However, with our climate the French name for these lepodopterans is Chenille à tente estivale, “worm who puts up a tent in the summer time” seems a bit preemptive.

Hyphantria cunea is common all over North America but in it's most northern range, Canada, it only manages to get in one life cycle per year. The insects over winter in pupae attached to fallen leaves and emerge in the spring as adults. The adults mate and then the females lay their eggs on the underside of leaves covering them with silken threads. The eggs hatch and the party begins, munching their way through foliage at an alarming rate. While they eat they excrete silk to create a protective nest. They can often be seen grouped together in their nests early in the morning or on cold days. Typically the host plants for these indiscriminate feeders includes, apple trees, balsam poplars, choke cherries, pin cherries, trembling aspens, white ashes, white birches, white elms, and most willows.

Typically the damage is mostly cosmetic, especially when you consider that the trees have already gotten some energy from the leaves and within a few weeks of lose them. These insects rarely eat all the leaves on a tree and seem to only enrobe a branch or two for their harvest festival.

If you have the stomach for it you can remove the nest by hand or with snippers in the morning and eliminate the problem. They are susceptible to a number of control methods including insecticidal soap or strong stream of water. Check the label on your product of choice or contact a professional to clean up these insects. Cutting out the webs when they are young is the preferred method, and be sure to bag them and dispose off site. A few hours in a black plastic garbage bag in the sun will eliminate any chance of them surviving. Tie the bag tight as they will try to escape and as I found out set up shop in the trunk of your car! If you thing you have this gregarious group dining on your prized specimens contact your Certified Arborist.