Have you noticed small yellowish-green worms seemingly floating in midair? Or have you observed small white spots on your grass, trees, or even your car? These floating worms are actually caterpillars called oak skeletonizers. These native, 5mm long, caterpillars get their name from the oak leaves they leave behind after feeding. Oak skeletonizers feed externally on the lower leaf surface leaving behind what looks like the leaf skeleton. Damage to oak trees largely goes unnoticed, except in times when large outbreaks occur. Even during years when the populations are high, the oak trees generally are left no worse for wear.
What about those white spots on your grass, trees, and cars? Those are the caterpillar’s cocoons. At only 3mm long, the cocoon will house the caterpillar until it morphs into its moth form. The moths are fairly unimpressive with dark 7-8mm wide wings and a paler body. These adults emerge in April or May and lay their eggs on the underside of newly emerged oak leaves. In Michigan there are two generations of oak skeletonizers. The caterpillars seen now are the second generation and should only last another week or two before they all form their cocoons. Control of these caterpillars is not necessary under most circumstances and they should be left to their natural life cycles.