Long-lived, with a life span of about 10 months, Mourning Cloaks are the first to appear in the spring after hibernating all winter.
Females lay eggs from early May to early July in the north using a variety of trees like elm, hackberry, poplar, birch farther north, but the females prefer willow. Eggs are yellow, and turn black before hatching.
Larvae are called the Spiny Elm caterpillar. When young, they usually stick together, all on the same leaf.
New batches of adult Mourning Cloaks appear about mid-June in southern Ontario, later up north. They will feed on flower nectar of milkweed, dogbane, boneset, butterfly bush and even boxwood flowers, but they prefer tree sap and rotting fruit.