Oak tree droppings

Asked June 29, 2020, 11:33 AM EDT

This year we have huge amounts small black seeds(?)dropping from our oak tree. They look like small pepper corns, and when wet, leave a stain. What are these? We also have an overabundance of small black caterpillars. Are the two situations related? What do the caterpillars morph into?

Newaygo County Michigan

1 Response

The two are definitely related! It sounds like your oak tree is likely infested with gypsy moths. They have been making a comeback this year. The small black caterpillars you are seeing will become larger as the season progresses. The small black seeds dropping like rain are the excrement of the caterpillars. As they much your oak leaves, hungry caterpillars release frass — or droppings — onto humans and cars, etc. from the trees above. If left on sidewalks, cars, etc, the frass can discolor. Crushed caterpillars also can stain driveways.

Control of the gypsy moth would need to have been done much earlier in the season. In the past, aerial spraying with Bt was used to control the gypsy moth.

Gypsy moth larvae are just beginning to emerge by May and are tiny and inconspicuous at that time. They often spin long silken threads on which they drop down from the foliage. The wind then helps disperse them to other trees. The larva feed in the canopy during the cooler night time and climb back down to hide in recesses of the bark or leaf litter during the heat of the day. Often you can kill them manually while they're on the bark or ground. Gypsy moth caterpillars can be so abundant that many trees will be completely defoliated by early July. Due to the size of oak trees, aerial control is the best option. This would typically be done in large areas at once, and can be fairly costly.

The links below will give you some additional information on this serious pest: