A moth that never eats, and a larva that looks like a small snake. Meet the regal moth and its larva, the hickory horned devil caterpillar.
The Hickory Horned Devil Caterpillar
Image credit: Bob Warrick. Used under a CC 4.0 license. The picture was taken in the Ozarks of Missouri.
The savage-looking creature in the picture, the hickory horned devil caterpillar (scientific name Citheronia regalis), presents no danger to the hand that holds it. Despite its fiendish name and ferocious appearance, the caterpillar has a benign nature. The sharp-looking horns do not pierce the skin. And though the caterpillar rears its head and shakes it menacingly, this insect can do no harm. Besides its appearance, the hickory horned devil has no defense against a predator.
The hickory horned devil is the largest caterpillar in the United States, and one of the largest in North America. It can grow to a length of 14 cm (5.5 inches).
This caterpillar develops into the regal moth (Citheronia regalis). The moth is one of the largest in the United States and may have a wingspan of between 9.5 to 15.5 cm (3.74 to 6.1 inches). The regal moth is also called the royal walnut moth.
The moth, however, is not the largest in the the United States. That distinction goes to the cecropia moth (scientific name Hyalophora cecropia), which is the largest in all of North America. The cecropia may have a seven inch wingspan.
Image credit: Brandyhouk. Used under a CC 3.0 license
Both the regal moth and the cecropia are in the Saturniidae family of moths. These moths are often nocturnal.
Image credit: Andy Reago and Chrissy McClarren. Used under CC 2.0 license
The regal moth will not live long, perhaps only ten days. In that time, it will not eat. It does not have working mouth parts, nor does it have a digestive tract. Upon emerging from the pupa, the female begins to exude pheromones. These will attract males, even if they are miles away.
Long Furry Antennae of the Male Help Him to Locate the Female
Image credit: Andy Reago and Chrissy McClarren. Used under CC 2.0 license.
Female Has Less Dramatic Antennae
Image credit: Shawn Hanrahan at Texas AM University. CC 1.0, 2.0, 2.5
The female regal moth carries hundreds of eggs. These she will deposit before her brief life, about ten days, has ended. She may even deposit some of the eggs before she mates. These sterile eggs will not hatch.
The male is equipped with claspers, to help him hold onto the female during mating.
Claspers, Closed, Male Regal Moth
Image credit: Megan McCarty, CC. 3.0 license.
Mating will occur on the second night after the moth emerges from the pupa stage. Egg laying will occur on the third night. The female will deposit between one and four eggs at a time. She will mate only once in her life, the male several times.
The moth will lay her eggs on a variety of host plants, including (according to the University of Florida Department of Entomology and Nematology): the pignut hickory, sweetgum, persimmon, and winged sumac trees.
Pignut Hickory Leaves
Image credit: Kristel Schoonderwoerd, used under CC 2.0 license
The eggs will hatch in six to ten days. This YouTube video shows two of the eggs hatching.
When the caterpillar emerges from the egg, it is black. It will go through four molts over a period of 35 days, and will change color as it molts. The final molt, called the fifth instar, is the turquoise phase.
The caterpillar's job is to eat. It is only in the larval stage that this species can feed. Once the caterpillar has reached maturity, it will burrow into the earth and pupate.
Unlike some other moth species, regal moths do not spin a cocoon. They overwinter underground as pupae.
This YouTube video show a hickory horned devil caterpillar shedding its skin and becoming a pupa.
The Regal Moth's Role in the Environment
Although the larval stage of the moth (the caterpillar) is quite large and has an appetite to match its size, this insect rarely does catastrophic harm to host trees. The regal moth is not considered a pest. It is, however important to the environment. Many birds, snakes, even bats feed on this species. It is an important part of the "food web".
Threats to the Regal Moth/Natural Enemies
The species is not endangered in the United States as a whole, but it is under stress in New York State. In that state, two gypsy moth controls have impacted the regal moth population: chemical spraying and the introduction of a parasitoid fly.
In addition to the many predators that feed on the regal moth, a variety of parasitoid flies and at least one parasitoid wasp (Cotesia teleae) are its natural enemies.
A few weeks ago I wrote a blog about toxic caterpillars. One thing I took away from that blog was, no matter how beguiling a creature may seem, it can be toxic. Then I came across this caterpillar, with its fearsome horns and nightmarish name. This insect is nonetheless benign. I was interested in learning more and thought I'd share what I learned.
I hope you found the post as interesting to read as I found it to research.