Saddleback caterpillars are one to one and a half inches long. They are distinguished by the large brown spot or “saddle” in the center of their back. Stiff, white hairs cover the sides and both ends of their body. These venomous hairs are the defensive armor of the saddleback. When they touch bare skin, a fiery welt rapidly rises. Brushing against one when walking past a tree branch or working among flowers can make several painful stripes on a cheek or hand.
The caterpillar feeds on leaves in late summer. It will soon pupate and overwinter on a dry twig. You can’t really do anything to get rid of them on a wide scale – insecticides would just kill lots of other bugs without appreciably lowering the number of saddlebacks.
The best defense is simply a pair of sharp eyes. Look before you plunge into your shrubbery to prune or to retrieve a garden hose. Watch out when you weed your flowers. Next spring, a brown moth with black streaks on her wings will hatch and begin the process again.