Unwelcome tent campers...

Something bright caught my eye as I drove through the woods, causing me to stop the car and check it out. It was about mid-way up the tree, just about eye level. As I approached, I could see a web of silk filled with small, dark caterpillars spanning the fork of a maple sapling branch. I recognized it as a tent caterpillar, an insect that is capable of totally defoliating a tree. There are two species in Pennsylvania; Eastern Tent Caterpillar Malacosoma americanum and Forest Tent Caterpillar Malacosoma disstria. Eastern Tent Caterpillar arrives in the spring, while Forest Tent Caterpillar returns in autumn.

It's important to make the distinction, because one is worth controlling while the other is not. Any time a deciduous tree is defoliated early in the growing season, it's more serious than if it occurs later. Just as squirrels store food before winter, trees store food in their roots during winter. This provides the energy needed to leaf out in the spring. Once leaves unfold, trees begin manufacturing their own food again (carbohydrates and sugars) through the process of photosynthesis. When autumn frosts arrive, trees send this food back into "root storage".

If a tree is defoliated by tent caterpillars as the foliage appears in spring, it's forced to leaf out a second time before its had a chance to make more food. This process depletes food reserves even further and leaves trees vulnerable if there is additional stress during the growing season. Think other insects, hail damage, frosts, diseases - any number of things can happen.

If caught early, and the tent is within reach, you can either squish the insects in their tent or prune the tent out. If the tent occurs where structural branches connect, is out of reach, or you are squeamish about the squish factor, consider spraying with Hot Pepper Wax. There's no need to wait for the insects to emerge from the protection of their tent at night to spray. Simply saturate the tent with Hot Pepper Wax Insect Repellent any time during the day and these caterpillars will be "fumigated" within their tent.

With rare exception, there's no need to spray the Forest Tent Caterpillar that appears in the fall. Since they damage trees just before they'd naturally drop their leaves, the trees have already made enough food for winter and won't be seriously hurt. No major harm means no control needed and more time to enjoy your garden.

Eastern Tent Caterpillars - May 2012