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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Silkmoth Season, Part 2: A royal welcome – Royal Walnut Moth, Citheronia regalis

 

 Adorned with horns and almost six inches in length, the Hickory Horned Devil is harmless unless you are a hickory tree.

 

This is the largest pupa I've ever seen! 

Last week we met the Imperial moth, one of most noble members of the Lepidoptera clan.  Today we visit another regal beauty, the Royal walnut moth. A few years ago our bug-centric neighbors presented us with a rather large, dark, cigar-shaped object discovered in the duff beneath a walnut tree in their back yard. With the comment “it moves” came the question “what is it?” Not many insects in Maryland form a pupa that can fill a hand, but this one did. The confiscated pupa took up residence on the kitchen counter for a month or so until one morning a vacant pupal case was replaced by a very impressive moth clinging to the sofa in the family room. The Royal walnut moth is also known as the Regal moth for obvious reasons.

 Female (above) and male (below) Royal Walnut Moths make a regal couple indeed.

In Maryland, only one generation of Royal walnut moth occurs each year. Life is short for giant silk moths such as this. Unlike its relatives the butterflies or hawk moths, silk moths lack functional mouthparts and do not eat as adults. They live only a few days. Their sole mission is to find a mate, do so, and lay eggs in a suitable place before being discovered and eaten by a bird or another hungry predator. To attract a mate, a female moth releases powerful chemicals called sex pheromones. Usually, this takes place on an upright structure, such as the trunk of a tree, on the night following emergence from the pupal case. Usually, this takes place on an upright structure, such as the trunk of a tree, on the night following emergence from the pupal case.

From her royal chamber, the female Royal Walnut Moth releases her pheromone to attract a mate. 

Not wishing to stand in the way of true love, but concerned that this magnificent princess would be eaten by a bird, the Royal walnut moth was confined in a predator proof bridal chamber, in this case a squirrel proof bird feeder, and placed outside to attract her mate. Her pheromones were strong and apparently irresistible. In her chamber the following morning was a male Royal walnut moth. Shortly after the royal couple completed their connubial interlude, the female left her chamber and began to deposit eggs on almost every surface she encountered. While taking a momentary rest on my leg, she treated me to eight large eggs just above the ankle. The eggs of the Royal walnut moth are typically laid on leaves of a tree suitable to meet the nutritional needs of the developing larvae.

Leaves of walnut and hickory are favored sites for Royal Walnut Moths to lay eggs.

Eggs hatch in about a week and the larvae develop into one of the most striking caterpillars on the planet, the Hickory horned devil. This giant of the silkmoth world may attain a size of five to six inches when fully grown. Favored hosts are plants in the family Juglandaceae such as walnut, butternut, and hickory. Hickory horned devils have also been recorded eating ash, beech, lilac, persimmon, sumac, and sweet gum.

Horns of the recently hatched Hickory Horned Devil are almost as long as its body. 

Fortunately, the male performed his task admirably, and after a few weeks, dozens of small devils hatched from the eggs. The task of feeding this many hungry mouths soon exceeded the time budget of this bug geek and after a couple of weeks and a few quick molts, the caterpillars were emancipated to several walnut and hickory trees on the College Park Campus. Perhaps, the wisdom and beauty of a creature that has transcended epochs of change on our planet will impart some of the same to this year’s incoming class of freshmen.

References

Thanks to Jeff and Linda for providing a great subject for this episode of Bug of the Week.

For more information on Royal walnut moth and Hickory horned devil, including information regarding rearing silkworm caterpillars, please visit the following web site:

http://www.butterfliesandmoths.org/species/Citheronia-regalis