‘Social' Caterpillars Eating Their Way Through Our Trees

If you like to get shade from that tree in your yard, you might soon be at odds with a hungry caterpillar.

It’s feeding time for the Eastern Tent Caterpillar. You may have noticed them setting up shop in tree branches in your neighborhood. The black colored insects build fuzzy, odd-shaped forts around tree branches, close to their favorite food: leaves.

The caterpillars, native to our area, recently hatched from their eggs and are focused on growing ahead of their metamorphosis into moths. For about six weeks, the larvae chew their way through leaves morning, day and night.

Unlike other caterpillars, the Eastern Tent are a social bunch, hanging in groups says Greg Cowper, an entomologist with the Academy of Natural Sciences of Drexel University.

“It’s unusual for caterpillars,” he said. “They eat together; they literally leave the tent in the morning and have breakfast on the leaves and then come back to the tent before going back out for lunch.”

The groups average about 15 to 20 caterpillars, which means they can put a pretty dent in the amount of leaves they mow down.

The tents they form are made from silk spun out of the caterpillar’s mouth and the bigger the group, the larger the tent. Cowper said they use the home as a way to regulate their body temperature.

“Throughout the day they’re moving to different parts of the tent based on how hot or cold they are,” he said.

They also hang together to keep predators like wasps and flies away. When a threat is nearby, all of the caterpillars violently shake their heads at the same time, making it tough for the insects to lay their eggs on the caterpillars.

While the caterpillars can decimate tree leaves, they’re nothing more than a nuisance. A short-term one at that. Cowper says the caterpillars typically cocoon after that six week eating period, before turning into moths, mating and then dying.

Trees usually bounce back once the eating assault is over and regrow their leaves.  But if you just can’t stand them, you can take matters into your own hands – literally.

“In my neighborhood, we go around often and just rip them out of the tree and throw them into a bucket of soapy water,” he said.

The soap keeps them from escaping the bucket and they drown. You could also dump the soapy water on the tree tent as well or use the natural insecticide BTK.

And those looking to prevent the caterpillars from coming back next year can cut down egg cocoons of laid by the moths.