Walnut caterpillars are producing noticeable defoliation in southwest Ohio. The moth caterpillars feed in groups, or "colonies," of 10-30 individuals throughout their development which is why their defoliation is often focused on a single branch or a group of adjoining branches. However, it's also why multiple colonies can quickly defoliate small trees.
This is the time of the season when Yellownecked Caterpillars can rapidly defoliate trees. Yellownecks feed in groups, sometimes called "colonies," numbering 10 – 30 individuals throughout their development. They are now reaching maturity meaning these gangs of large caterpillars can devour leaves at a rapid pace.