Inchworm Irruption

You can't walk through the woods these days without seeing lots of inchworms, and what sounds like rain is actually their poppy-seed-like droppings hitting leaves on the ground.

Last year was the first year we experienced them in explosive numbers, a cyclical phenomenon known as a population irruption. Occassionally having a population explosion helps some prey species outnumber their predators, ensuring long-term survival. An irruption can also be an indicator of natural balances being disturbed.

Indeed, last year the woods were stripped of leaves in May, and it looked like winter all over again. But the trees leafed out again. This year the inchworms haven't stripped the trees bare, yet. In this photo they were congregating all over a rotting tree stump.

The "inchworms" are likely fall and spring cankerworms (Alsophila pometaria and Paleacrita vernata), the larval form of species of moths. The youngsters feed on leaves, pupate in the ground, and adults emerge in fall or spring to lay eggs. The female adults of these native species are wingless, and climb back up the tree trunks to lay their eggs.

Thanks to Erich Estes for researching these insects last year.