Summer World_ A Season of Bounty - Bernd Heinrich [50]
Cecropias emerge from their pupae as adults when they shed their pupal “skin” (strictly, an exoskeleton), and then they crawl out the escape hatch of their cocoons around noon on any one day in May. The freshly emerged moths then hang stationary, expand their soft flaccid wing stubs (the outlines are visibly inscribed on the hard pupal exoskeleton), and inflate them with blood to stretch them until they have expanded to full size. The still soft fresh moth then releases a hormone from the brain that activates a hardening agent, and the wings then become frozen into their final shape. When eclosion—the act of emerging from the pupa, which is triggered by hormones—is finished, the moth then purges its gut. What is purged, the meconium, contains fecal and urinary wastes that had accumulated during the pupal stage (which lasts more than ten months); in the females, the meconium also contains the sexual attractant.
Males, who search for females solely by their scent, may come from miles away, flying upwind. Mating in this species begins just before sunrise and lasts about fifteen hours. (Most of the “mating” time is actually guarding, in which the male prevents another male from mating with his female.) Egg laying follows immediately, and the female then flies every night for about a week to scatter her eggs in clusters. They are coated with a glue and when deposited stick to the leaf undersides of several species of forest trees.
The larvae hatch after about twelve days, near 1 June, and then they grow through five stages. Each of these “instars” is separated by a molt. The first larval instar is black and is covered with orange and black tubercles. The second has bright orange and black spots. The third is yellowish green with black spots and blue tubercles. The fourth is light green with a broad dorsal band of blue and yellow, coral and black tubercles. The fifth larval instar is also light green but with a dorsal band of only blue. After each molt the larva eats its old, shed skin, except for the spines and tubercles.
By mid-July the mature larvae stop feeding and initiate violent gut peristalsis that empties them. They are then restless and wander, often leaving the food plant. They eventually stop wandering and begin an incessant labor of about a week, by day and night, to spin the cocoon. First a larva makes the outer shell, leaving an exit valve for the moth’s eventual escape. It then makes the inner cocoon layer by rapid zigzagging sweeps of the head—all except for the threads at the exit valve, where it lays down the silk in parallel lines with the long axis of the cocoon. The larva keeps turning from one end of the cocoon to the other, first laying down silk and then saturating the entire structure with saliva that cements the threads together and makes the cocoon tough and waterproof. The cocoons of this species are unique in having two layers, an outer and an inner section, and an escape hatch at one end for the moth to emerge from during the following summer. The double case probably helps to protect the defenseless pupa from predators; a would-be predator has to invest considerable effort to penetrate even the first, outer wall, and if it manages to do so and then finds only another wall, it may leave.
After working ceaselessly for several days to finish the cocoon, the caterpillar orients itself within this cocoon so that its head faces