In late summer, when the birds are quiet, and the hum of cicadas is the only sound to be heard along the hot woodland trails, a quiet migration is occurring.
The migration of fall warblers has started, but many of these birds are still in New England and passing through Cape May on their way south to their tropical wintering grounds. Hummingbirds are quite visible, feeding nonstop in preparation for their journey, Eastern tiger swallowtails are nectaring, and dragonflies fill the air.
Still, there is something more in the woods that has my attention. I linger by the sweetgum and persimmon trees in search of the formidable hickory horned devil.
The name of our largest American caterpillar is as threatening as the appearance of this giant.
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Many caterpillars have strong defenses. Many have stinging hairs, some are bad tasting. Some caterpillars even sport white spots that resemble the eggs of the parasitic wasps that prey upon caterpillars, as if to hang an “occupied” sign on their backs.
But the hickory horned devil has taken defense to an entirely new level.
It begins life hatching out from the surface of its host plant leaf. That may be a hickory or black walnut, but here in the South, the parent regal moth will frequently use the persimmon or sweetgum. In its first instar, the caterpillar will look like nothing more than a darkish bird dropping. Remember that in spring and summer, birds raising their young depend upon the protein, fat-packed nutrition of caterpillars to feed their broods. Very few caterpillars of saturniid moths have any chance of escaping the sharp eyes of hungry birds.
By late August, a few hickory horned devils have reached their fifth and final instar before pupation. The creature measures over five inches long, has taken on a minty turquoise hue, and sports an array of threatening spikes and knobs in black and orange. If you approach this demon, it lashes its black-spiked head towards its aggressor.
The appearance of this caterpillar brings to mind a smaller version of a Chinese New Year dragon. It is entirely harmless. The threatening spikes are soft to the touch, and the skin is soft and pliant. The disguise is very successful. No amount of reassurance can convince most people to hold the hickory horned devil in their palm. The usual response when someone encounters one is a gasp, and the exclamation, “What IS that thing?”
By the time we get to see a hickory horned devil, either low in a persimmon tree, or wandering on the ground, the caterpillar has worked its way down its host tree, to drop to the soft ground in search of a place to bury itself and pupate. Unfortunately, the poor devil has one more obstacle to overcome. Copperheads wait on the ground. They are generally ambush predators, but will actively hunt for caterpillars and cicadas in the leaf litter. A few caterpillars will manage to pupate, but some of these pupae will fall victim to tachinid flies laying their eggs in the pupa.
Surviving pupae overwinter beneath the ground, and will emerge the following year, pumping their wings on the ground and flying up to the canopy for a brief few weeks as the exquisite regal moth. Sometimes in late July, you may be fortunate enough to see one that has been attracted to the bright lights of a rural gas station.
Adult regal (aka royal walnut) moths have gray-green forewings with orange veins, and a row of seven to nine yellow spots. The body of the moth is bright orange with yellow banding.
It is a rare treat to see either the moth or the hickory horned devil. Throughout its range, their numbers are declining. They aren’t agricultural pests in any way, and their numbers are too few to do any damage to host trees, so they should be never be harmed if encountered.
For all my wanderings in the field over the years, I have encountered only one in my lifetime, but as summer ends; I am back searching, hoping for another chance to encounter this alien beauty.
Mary Sonis is a naturalist, photographer and writer in Carrboro. You can reach her at firstname.lastname@example.org