By Ashton Nichols
Yesterday morning, while I was pushing my granddaughter Verona on the swing in one of our large cedar trees in front of Creekside, I noticed a sudden flash of yellow against the striated brown bark of the tree’s massive trunk. As I drew closer, I could see that it was two Imperial Moths (Eacles imperialis), beautiful members of the silk moth family, the group that produces the largest moths found in North America. These two were clearly mating, joined at the hind-parts and perfectly still, presumably waiting in their nocturnal way, at least for the sun to go down.
Moths can take a full 12 hours to mate. The male’s goal is to pass a spermatophore into the female’s body, so that she can then fertilize her eggs. He has located her by sensing her pheromones in the nearby air and then flying toward the source until he locates his partner. Once together, the moths unite by backing up, abdomen to abdomen until they are firmly joined. Then the male clasps the female with small, finger-like appendages– “claspers”–so that the two can remain connected, even if they have to move from one spot to another during their prolonged “romance.” Research indicates that a mating pair like this, hooked together and unable to separate until their work is done, are especially liable to predation, often by raccoons and other small forest mammals.
These two insects that Verona and I watched today were gorgeous and large examples, a full five inches across from wingtip to wingtip, the female slightly larger than the male. Their bright yellow wings were patterned with a brown that almost shaded to purple; they had a thumb-thick and sharply segmented abdomen, and a wide, furry head and face. The female has a unique–if invisible–anatomical feature, her “bursa copulatrix (literally, organ for “exchange coupling),” where she will store the spermatophore that she receives from the male. This tiny packet of his genetic material also contains nutrient materials to keep the fertilized eggs supplied with “food” in her body, not unlike the way an egg’s yolk and white support the growing chick.
Here is how complicated and technical the entomologist’s description of the Imperial Moth can get: “Both sexes have round, purplish to reddish-brown reniform and subreniform spots on the forewing, the center of each spot filled with gray; as well as a similar discal spot on the hind wing” (this drawn from the Massachusetts “Natural heritage Endangered Species Program”). The last century has seen a dramatic decline in species range and numbers so that now, in Massachusetts for example, the moth–which once covered the state–is only found on Martha’s Vineyard Island and occasionally on the nearby mainland. In our part of Pennsylvania the decline is less pronounced, but the Mason-Dixon line seems to be the dividing line: Imperials in Maryland and south tend to be doing much better than their northern kin.
So there we were, on a warm July afternoon with a single species of declining moth, bringing knowledge to me and wonder to my wide-eyed, three-year-old grandchild. “What are those two moths doing, Baba,” Verona said, with her eyes still wide and staring. “Well, my little girl, they are resting . . . um, ah, ” pause, think, speak: “and they are starting to make babies for the next generation . . . I, uh . . . I mean for their next family of beautiful moths.” “They ARE beautiful, Baba,” Verona said as we turned to come into Creekside to get the camera.
This morning I returned and the pair was gone: he to feed and hopefully to survive a few more months until winter, she off to lay her fertilized eggs and begin their remarkable metamorphic moth lifecycle again.