Spiny oak sawfly creates two types of defoliation. Young larvae chew holes in the leaves, and older larvae feed on leaf material between the veins. There are 3 sawflies near the center of this photo.

Spiny oak sawflies are one of the many things that will feed on oak leaves. Sawflies look like caterpillars but they aren’t, so the caterpillar-specific pesticide, Bt, will not be effective on them.  Spiny oak sawflies feed between the veins of the leaves, leaving a lacy appearance to the leaves.  They have forked spines all along their bodies which turn black as they get older. I’m not aware of this ever being much of a real problem but at one site in Price County the damage to understory oaks was significant.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.