What are those web like things on tree branches?


You know, these things. (Credit: Alison Hunter)

If you live just about anywhere in the US, you’ve likely noticed weird things that look like a really intense spider web or maybe some sort of cocoon on the tips of tree branches in the late summer or early fall. They often seem to be clumped together with several on one tree, and they show up all over the place at the right time of year. So what are they?

The culprit is the Fall Webworm, which is actually a type of moth. Moths will lay hundreds of eggs on the underside of tree leaves. About a week later, the eggs hatch into small, hairy caterpillars, which begin eating the leaves and other parts of the tree. As they do, they build a big, silken web, which encloses and protects them. This web catches bugs, leaf remains, and even caterpillar droppings which gives it its characteristically nasty look. By the time winter comes around, the caterpillars wrap themselves in cocoons in order to survive the winter. They hatch in the spring in order to breed, lay eggs, and start the cycle all over with more nasty-looking webs.

BONUS: The Penn State Agricultural Sciences Extension page on the Fall Webworm states, “Warning: Pesticides are poisonous.” I thought that was kind of the point…

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