Redhumped oakworm

Defoliation of bur oaks and other oak species was reported in Hubbard and Becker Counties during late August and September. Redhumped oakworms, Symmerista canicosta, consume all of the leaf tissue except the major veins. This was the third year defoliation was noticed, and, interestingly enough, different stands were affected each year.

These oakworms overwinter as pupae in the duff beneath the trees they?ve defoliated. Moths emerge the next summer from June to late August. Eggs are laid on the undersides of host leaves and caterpillars feed in colonies. On the back of each caterpillar, there is a large reddish bump which gives this species its name.