It’s hard to imagine a more wonder-inspiring group of animals than the giant silkworm moths of the family Saturniidae. Anyone lucky enough to encounter one is left awestruck with a memory of the natural world that will last a lifetime. They are among the largest insects in the U.S., some with wingspans topping six inches, and are decorated with brightly colored, velvety scales of a myriad of colors, from lime green to bright pink.
Among the most impressive of these iconic denizens of the night is Citheronia regalis, known variably as the Regal Moth or Royal Walnut Moth. This species is, by mass, the largest moth north of Mexico. They can be found throughout much of the eastern U.S., where they occur in mature forests with a large hardwood component. They are generally uncommon throughout there range, and appear to be declining in many areas, likely due to a number of factors including habitat loss, pesticide use, and increased urbanization which creates “light traps”, where moths are attracted to artificial lights and perish prior to laying eggs.
I was lucky enough to find the relatively fresh individual pictured below resting below the lights in town. I brought her to a more remote area where I hoped she might mate, or if she had already mated, find a suitable location to lay her eggs.
The life of an adult silkworm moth is both romantic and tragic. After emerging from their pupae, the clock is ticking to find a mate. Most species only have vestigial mouth parts, and are unable to feed. Others do have weakly functioning mouth parts, but still generally do not take food. Shortly after emerging, females begin filling the air with pheromones, which spread out like chemical tendrils in the night air. Males may pick up these cues from great distances, and will follow them to the females so that they may mate. The females then find a suitable host, and lay their eggs. Within a week of emerging, they are dead.
Regal Moths will utilize a variety of hardwoods, but display a real affinity for hickories (Carya spp.). The larvae are among the fastest growing organisms on the planet, and will increase in mass by thousands of times from hatching to the point they are ready to pupate. As they grow, the caterpillars spring barbed spines and take on an appearance so formidable that it has earned them the name “hickory horned devils”. These spines are purely for show, and they do not sting and contain no toxins. When threatened, however, the caterpillar may rapidly swing its head from side to side in an attempt to strike a would-be predators.
The caterpillars start off brown and gradually turn green with each molt. Finally, when they are ready to pupate they take on a bright turquoise hue. At this point they may be as much as six inches long! Unfortunately I have never encountered one of this size and color with camera in hand, but I do have an image of one in the brown stage from a few years ago.
Encountering any silkworm moth is a special experience, but spending time with the beautiful Regal Moth is one I will forever cherish. Like all other organisms great and small, our lives are richer because they exist.