A male mourning cloak butterfly basks in the sun on an eastern hemlock while its dark wings act as solar collectors, warming the hemolymph (a circulatory fluid analogous to blood) in the wing veins and returning the warmed fluid to the butterfly’s body until it reaches a temperature sufficient for flight. This butterfly has just emerged from hibernating in a sheltered spot, such as behind loose bark. Because they overwinter as adults, mourning cloaks are one of the first butterflies to be seen in the spring. The adults mate and lay eggs, and the caterpillars that hatch from the eggs will metamorphose into adults in June or July. After feeding for a short time, the adults become dormant (estivate) until fall, when they re-emerge to feed and store energy for hibernation.