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By Root 1226 0

caterpillars living near the North Pole are surely exotic, and very few people get to see them (I was one of the lucky few who was invited by Jack Duman and Olga Kukal, two colleagues from the University of Notre Dame, to travel north to study them). However, there are also marvels at one’s doorstep. At the farm in Maine, I collected nectar-sipping sphinx moths humming around the milkweeds by the barn. Later, my mothing took me to Los Angeles, where in the lab of George Bartholomew at the University of California, I tried to decipher if and how they regulated their body temperature. A couple of decades later I came full circle and returned east and discovered winter moths for the first time. These winter moths are not seen by the average person—only by those who go out into the woods at night with a bucket and a brush and paint trees with an ambrosiacal concoction of fermenting mashed fruit (apple, banana, or peach will do) spiked liberally with beer or some other alcoholic beverage. Each lepidopterist has his or her own special concoction that works best, which I suspect has as much to do with individual taste as with science.

Adults of the winter moths (Cuculiinae) don’t just survive the winter in torpor. They live as adults in the winter world. There are numerous species of these moths belonging to the Noctuidae, or owlet moths, which is possibly the most species-rich group of Lepidoptera on earth, with thousands of species in temperate and tropical regions. The cuculiinae are distinguishable from other noctuids primarily by their so-called reversed life cycle. Whereas the vast majority of moths overwinter as pupae, the cuculiinids overwinter as adults and they also fly during the winter thaws when temperatures reach near or slightly above the freezing point of water. By mating and then maturing their eggs in the winter and laying them on the just-opening leaf buds in early spring, the adults are less likely to be eaten by bats, and the larvae also encounter less bird predation, since growth to the pupal stage can be finished before their predatory migrants return to reoccupy the northern woodlands.

Like sphinx moths and other noctuids, these winter moths have robustly built thick bodies powering short wings that require a high wing-beat frequency to support flight. In order to generate sufficient power for rapid wingbeats they must warm up their musculature to over 30°C. They do that by shivering. A shivering moth extends its antennae, raises its wings, and then you see wing vibrations as the upstroke and downstroke wing muscles are activated nearly simultaneously. A covering of thick insulating scales on the thorax acts, like fur or feathers, to approximately half their rate of heat loss. Further heat retention from the working thoracic flight muscles is enhanced by countercurrent mechanisms of the blood circulatory system that reduced heat loss into and from the abdomen. These moths are unique in their willingness and ability to start shivering when their muscle temperature is as low as 0°C. (Most others require 15° to 20°C higher temperatures.) Once shivering begins and the muscles begin to warm up, then shivering proceeds more vigorously, to produce even more heat until the suitably high muscle temperatures needed for flight are attained.

THE LEPIDOPTERA DEMONSTRATE diversity of adaptation to winter within a single group. However, a discussion of frost-hardiness must necessarily include a specific and very famous maggot, that of the goldenrod fly (Eurosta solidaginis). Eurosta is as necessary to an understanding of insect frost-tolerance as the fruit fly Drosophila is to genetics.

As implied by the name, the fly’s life cycle is inextricably bound to the goldenrod’s. The adult fly injects an egg into a young and rapidly growing goldenrod stem in the spring or early summer. Chemicals that are either injected with the egg or produced by the young larva then subvert the plant stem’s normal growth, causing it to produce a thick tumorlike growth, called a gall. The gall has soft tissue on the inside, and is enclosed