Summer World_ A Season of Bounty - Bernd Heinrich [49]
10
Cecropia Moths
22 June 2007. THE TREES ARE FINALLY FULLY LEAFED OUT and have completed most of their twig growth now, and—more noteworthy—the buds that had produced the twigs with new leaves have in some species also already produced the buds for next year’s growth. And a few of these new red oak buds have already “broken” to produce a second spurt of twig and new leaf growth a year ahead of the others on the same branch. There is now ample foliage, and the giant silk moths have laid their eggs. I pick up a dead luna moth in the woods. Its pure white body “fur” contrasts with its fresh leaf look from its large, pale greenish blue wings. One of its two “tails” has broken off and the edges of its delicate wings are frayed from its hectic flight during the last week’s nights—the only time allotted to it as an adult. This is the only narrow window of time that one can meet these gorgeous creations as adults. This moth’s abdomen is shrunken—it had managed to lay its eggs, and its green caterpillars are probably hatching and starting to feed on the new oak, maple, and birch leaves.
IN HIS MASTER’S THESIS, A STUDENT, FRANK L. MARSH, wrote: “About the middle of March, 1933, the writer chanced upon an area within the limits of southwest Chicago” in which he discovered the cecropia cocoons (structures of silk made by caterpillars to hold and protect the pupa—butterflies don’t have cocoons) visible by the dozens on any one tree. In conversations with several people who had lived in the area for years, he learned that the cocoons had “always been just as thick.” But he wondered why they were not even more common, since each female moth lays 200 to 400 eggs. Marsh surmised that the moth population had achieved and was maintaining a state of equilibrium, in which births equaled deaths. He then proceeded to study possible mechanisms for maintaining such an equilibrium. He concentrated on the causes of death that could be deduced from the contents of the 2,741 cocoons that he collected. His was a project that I can scarcely conceive of, since I feel lucky to find even one of these now very rare cocoons; I have seen perhaps three in the last five years.
With all the abundance of the northern forest caterpillars, it is easy to forget that most of them turn into moths (primarily of the families Noctuidae and Geometridae). Not only are the moths much rarer than their larvae—there is perhaps only one moth per 100 larvae—they are almost all nocturnal. Summer nights belong to the moths and fireflies. The difference is that we see the fireflies. I “see” the moths only in my mind’s eye—especially the big ones of the family Saturniidae, the giant silk moths, which can be easily mistaken for bats when they fly in the dark. We know they are out there mainly because we may find their caterpillars in the summer, and for several species, such as the cecropia moths and the prometheans, also their cocoons in the winter.
The woods of New England contain (or contained) an abundance of half a dozen species of the spectacular saturniid moths. All of them are decorated in striking color patterns and clothed in a fine, though thick, velvety “fur” (modified scales, technically pile) that not only gives them their bright and intricate color patterns but also insulates them after they shiver to warm up to get ready for flight.
The cecropia moth, Hyalophora cecropia, is the largest of the local wild silk moths, and its cocoon is a brown baggy spindle-shaped structure. Although these moths’ caterpillars have been tried for commercial silk production, they have been used much more successfully as laboratory animals in numerous studies that have revealed secrets of the physiological connections of neurons and hormones affecting behavior, development, and metamorphosis. The Harvard biologists Carroll Williams, Jim Truman, and Lynne Riddiford are legendary and strike me as scientific shamans because of their extraordinary clever and revealing experiments, which delved deeply