Late fall oak caterpillar causing nuisance

Got tiny caterpillars dangling down on threads and laying tiny, white, rice-like cocoons everywhere? Sounds like you have a bad case of oak skeletonizer!

Ordinarily, tree insects are not very active this late in the autumn just prior to leaf fall, but there is one insect that is very abundant this fall and creating a lot of nuisance for many homeowners. It’s called the oak skeletonizer.

If you have seen a lot of very tiny, greenish caterpillars (about 3/8- to 1/2-inch long) dangling down out of trees on a thin thread of silk, it’s very likely it is the oak skeletonizer. Certain portions of the northern Lower Peninsula are exhibiting large populations of this insect. While this insect does not cause a great deal of harm to oak trees, it is more of a public nuisance between the caterpillars crawling around on people who “catch” them walking outside or from the tiny, whitish cocoons resembling small grains of rice that they deposit on many outdoor surfaces from vegetation to outdoor furniture and decks to even automobiles parked under trees.

What people are experiencing is actually the second generation of this insect this growing season. There was an earlier first generation that hatched in mid-summer. Oak skeletonizer is a native insect to our oak-dominated forest ecosystems. As such, peak populations occur every five years or so, but collapse down to lower population levels after a season or two. Because oak skeletonizer has evolved over time with our forest, there are natural predators, parasites and weather factors that eventually cause populations to fall.

If you were to look up into the canopy of an oak tree, it is possible to spot the leaf damage caused by these insects. Many oak leaves still attached to the tree will transmit sunlight right through the feeding damage on the leaf surface caused by this caterpillar – almost as if looking through “tiny windows.”

Unfortunately, there is really no control recommended for this insect, especially this late in the growing season. Removing the cocoons from this oak skeletonizer can be quite difficult at times. So many homeowners will likely just have to “grin and bear it” and wait for populations to collapse. In all reality, this insect is really more of a “people-problem” (i.e., nuisance) than it is a threat to tree health.

Related resource: Common Oak Defoliators in Michigan (It’s not always Gypsy Moth!), MSU Extension bulletin E2633