Late summer/fall is prime time for many caterpillars.  Yellow neck caterpillar is a leaf devouring creep that may affect several species of trees.  Adult moths emerge in late summer, mate, and lay eggs on the undersides of leaves.  Soon after the eggs hatch, and the young feed in clusters on branch tips.  After a few weeks of feeding the caterpillars fall to the ground, where they bury themselves in the soil to pupate.

These caterpillars usually only cause peripheral damage, and most often treatment is not warranted.