What insects can you possibly find outside in November? When most leaves have fallen, I suggest searching for cocoons!
Many small moths spin their cocoons underground, hidden from sight. However, members of the giant silk moth family—Saturniidae—attach cocoons to branches above the ground. Cecropia is the largest moth species, constructing a brown pod resembling a dead leaf cluster. Pointed at both ends, the five-inch-long cocoon feels like wrinkled paper. The cocoon remains intact from autumn until the following spring in a suspended growth state called diapause.
How did the cecropia get to this stage of its life?
Longer daylight in May triggered the pupa inside the cocoon to change into an adult insect. A valve at the top of the outer layer and a second valve on the denser inner layer allowed the crumbled adult to safely exit, usually mid-morning. The moth slowly inflated its six-inch wingspan, showing the brown, beige, and orange design with four crescent-shaped spots. Orange hairs cover the body. The nocturnal adults live for about two weeks and do not feed.
Focused only on breeding, moths find each other by smell rather than sight. A female emits her pheromone of microscopic airborne scent particles, luring males from up to a mile away. A male’s feather-like antennae pick up the scent. The female can be recognized by her less-bushy antennae and well-rounded abdomen.
Females lay two to six eggs in rows on both sides of leaves. Host trees include maple, box elder, cherry, apple, birch, or dogwood. Eggs hatch within 14 days.
Young caterpillars grow through five colorful larval stages called instars over 60 summer days. First instars are black and bristly. Second instars turn orange with rows of black spots and bristles. Third instars become bright green with red, yellow, and blue tubercles and rows of black dots. Fourth instars change to bluish-green and lose the dots. Fifth instars grow to four inches long, and their droppings (frass) come out in star-shaped cylinders rather than rounded balls!
After purging its gut, the caterpillar stops eating. It begins spinning white silk from the abdomen. Days later the cocoon’s fibers darken, hiding the metamorphosis from larva to pupa. The pupa rests for eight months—wrapped in a silk blanket.
The royal treatment. The Saturniidae family was named for the Roman god Saturn because these large colorful moths seemed to be the royalty among their mostly drab moth relatives. The cecropia moth, Hyalophora cecropia, is named for King Cecrops, the first king of Athens who was half human and half snake.
In and out of hiding. Cecropia moths live throughout North America, from Canada to Florida and from the Atlantic Coast toward the Rocky Mountains. Observing this common species can be difficult because they fly only at night, although like other insects attracted to lights, you may see them flying near a porch light. The caterpillars are also challenging to find (in spite of their colorful patterns) because they hide under leaves during the day and feed mostly at night.
Facing foes. Human threats faced by the giant silk moths come from pesticide applications, loss of habitat, and urban lights. Natural predators of cocoons include squirrels, mice, and shrews. Many birds prey on the caterpillars, feeding them to their nestlings. Parasitoid wasps lay their eggs on the caterpillars, which hatch and live inside them.
Protected in silk. If you see unusual bumps on twigs or thick spots between forked branches, you may have found a cocoon. Overwintering cocoons naturally adapt to normal moisture and cold temperatures. They survive even the most severe Michigan winters, wrapped in their silk encasements.