Illinois Natural History Survey - University of Illinois

Species Spotlight: Cecropia Moth

Although the typical robins of spring spend most days eating worms, this "robin" eats nothing at all and wanders around in the moonlight. Known as the robin moth in England, in the United States this large silk moth is the familiar cecropia, Hyalophora cecropia. Cecropias are found in the eastern half of the U.S. except for the southernmost areas. In Illinois, cecropias are almost absent from mature woodlands; they prefer newly settled suburban areas with small shade trees. This behavior earns the moth the title of "fugitive species" because its populations are constantly shifting to disturbed areas. The reason for its preference for urban areas is simple--its major predator, the white-footed mouse, is absent. The house mouse, common in urban areas, cannot open the cecropia's cocoons and the pupae have a safe haven.

Cecropia moths emerge mid-morning from their cocoons during mid to late-May. Once the moth has emerged, it appears to be all head and abdomen. The wings hang limp and are wet and small. A resting place is soon found and the moth begins a pumping motion--forcing blood into its wings. Once the wings have expanded and hardened, they will be 5 to 6 inches across, colored a dark, red-brown with silver-gray highlights. The moth will then remain motionless for the rest of the day.

The Cecropia moth, Hyalophora cecropia.

Male moths will make a brief flight before dusk and then remain hidden until just before dawn when they go in search of a female. Females, heavy with eggs, remain where they are. Just before dawn, the female will send out a pheromone, an airborne scent that will attract the males. Using the scent receptors on his featherlike antenna, a male will follow the pheromone trail until he locates the female. They mate and remain coupled until the following dusk. Shortly thereafter, the male flies away and will search for another female during the next near-dawn period. The female moth, however, begins to lay large, oval cream-colored eggs in groups of three to six. The first eggs are laid near where the female originally pupated. After laying this first group, she flies away (the first time she has tried out her wings) and lays the remaining eggs on proper foodplants (far apart from each other to minimize competition for food among her caterpillars). Food plants include apple, white birch, white oak, black cherry, and several other tree species. The female will lay about 350 eggs. The adult moths have a life span of only 5 to 6 days and do not feed.

The young cecropia larvae are black and covered with bristles, and, unlike their parents, are eating machines. By late summer, the fourth and final instar larvae are large greenish caterpillars with four orange tubercles on their thoracic segments. When full grown, the larvae stop eating and descend to near ground level to spin cocoons among the stems of a shrub. This cocoon, the largest woven of any moth, has three layers--a tough leathery outer covering, a fluffy layer that suspends the inner within the outer layer, and an even tougher inner layer in which the pupae rest. The developing moths spend the winter in their cocoons and metamorphose the following year into the next generation of night-wandering robins of the spring.

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Last Modified 7/03/96

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