Saddleback caterpillars, Acharia stimulea, have a brown saddle-shaped spot on the middle of their green backs. They are called slug caterpillars because the abdominal legs lack tiny hooks that most other caterpillars have, and because the six jointed legs are so short. Saddleback caterpillars are one of the stinging caterpillars that bear urticating hairs on four prominent knobs at the front and rear as well as smaller knobs along the sides. These caterpillars are about 3/4 inch long when mature and spin tough silk cocoons in which they overwinter. Saddleback caterpillar moths are fuzzy and dark brown with some cinnamon spots and tiny white spots. These moths emerge from the cocoons the following spring and summer and lay 30 to 50 tiny, flat eggs that overlap like fish scales on the upper surface of leaves of various trees and shrubs. From the eggs hatch tiny, almost transparent caterpillars that already display yellow, spine-covered knobs around their bodies. Aside from tiny parasitic wasps that plague saddleback caterpillars, other mortality factors such as diseases and predators usually keep the numbers of these caterpillars low.