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ten-inch-long stem (petiole) of the leaf and—more important—onto the twig beyond. This beltlike strap of silk, on reaching the twig, is wrapped in a tight ring around it. By fall the leaf wrap dries and shrivels around the cocoon, and since it is “silked” to the twig it remains on the tree even after the leaf loosens its hold on the twig. Calosamia cocoons may hang from trees for several years, long after their contents have emerged and long after the camouflaging leaf wrap has disintegrated. However, despite all the protection that the cocoon provides from birds, the enclosed pupa is not safe from parasitoids. They have honed their attack strategy as much as the caterpillars have honed their defense.

There are a number of different ichneumonid parasitoids (predators that kill their hosts by eating them from the inside). One of them, Gambrus nuncius, is tiny and prettily red-colored, with white-ringed antennae. More than forty may emerge from a single cocoon. Another parasitoid, the large yellow-orange ichneumon Enicospilus americanus, is relatively rare, and only one individual ever develops in any one moth pupa. Others, mainly fly parasitoids, attack the caterpillar and emerge from it before it would normally spin its cocoon.

Fig. 23. Enicospilus americanus injecting an egg into a cocoon-spinning caterpillar, and the ichneumon’s development into the pupa.

On my hill in Maine, there have usually been enough Calosamia promethea cocoons for me to find ten to a dozen in an hour. However, I have never seen a female moth flying free in the woods; nor have I picked up a dead one. The moth’s life is restricted to about a week, and the whole population is active at the same time, in early June only. To see male moths is easier, but one needs to resort to a trick. Using a thread tied around her ample waist, I tether to a branch a female that has just emerged from her cocoon. By late afternoon males fly in, following the female’s odor plumes. I collected eggs from the mated females to raise the caterpillars.

The best time to find Calosamia, so as to raise them from eggs in the summer, is in the winter. After the deciduous trees have shed, the few individual leaves that remain are conspicuous and may be curled around and contain a cocoon. I keep an eye out for them on every winter walk in the woods. It has not been merely an idle pastime, because I justify it by hatching females from cocoons to tether onto twigs the next summer, and by trying to find out what parasitoids the cocoon contained or still contains. I collect about 100 or 200 cocoons each winter. In the winter of 2007 I made a thorough search of the same 300-acre patch of woods that I had perused in previous years, and managed to collect 359 cocoons.

For about ten years starting in the mid-1980s, I could always find cocoons containing live Calosamia pupae, although those infected with the Gambrus parasitoid were common, too. For a long time it didn’t make any difference to me how rare or common they were, but later it appeared that a pattern might be emerging, so I became more methodical and tried to find out if there was one. I found that through the years 1993 to 2006 the number of live moth pupae in cocoons decreased steeply from about 50 percent to less than 1 percent. Of the 359 cocoons collected in the winter of 2007 only 1 contained a live pupa! During the next winter (early 2008) I recruited my ten eager Winter Ecology students as Calosamia cocoon hunters. One student in particular developed an impressive record as a searcher, and all of us together retrieved 242 cocoons. Many were two-year-old cocoons I had missed previously, but in any case we found not a single current live Calosamia pupa, and only 1 contained a live parasite (Gambrus) pupa. In other words, the moths had now become at least locally extinct. We had collected the artifacts of a past population. We have no idea what caused the collapse, or why other giant silk moth populations have exhibited similar spectacular recent declines.

In western Vermont near Burlington, Calosamia cocoons have,