Earlier this spring our bug-centric neighbors presented us with a rather large, dark, cigar-shaped object discovered in the duff beneath a tree in their back yard. With the comment "it moves" came the question "what is it"? Not many insects in Maryland make a pupa that fills one's hand. We had a strong suspicion that this was one of the large silk moths in the family Saturniidae. The pupa took up residence on our kitchen counter for a month or so until one morning we awoke to find a very impressive moth clinging to our sofa. The royal walnut moth is also known as the regal moth for obvious reasons. Royal and regal certainly befit this beautiful creature.
In Maryland only one generation of the 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 other 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 their emergence from the pupal case. Not wishing to stand in the way of true love but concerned that our little beauty would be eaten by a bird, we placed the royal walnut queen in a predator proof bridal chamber and hung her outside to court.
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-bone. The eggs of the royal walnut moth are normally laid on leaves of a tree that will serve as a food source for the developing larvae.
Eggs hatch in about a week or ten days and the larvae develop into one of our most striking caterpillars known as hickory horned devils. These may be five to six inches long when fully grown. Hickory horned devils are commonly found on plants in the family Juglandaceae such as walnut, butternut, and hickory. They have also been recorded eating ash, beech, lilac, persimmon, sumac, and sweet gum. The remarkable pupa from whence this story began was discovered beneath a large walnut tree. If we are lucky and the male performed his task admirable, we will soon be blessed with dozens of small hickory horned devils. Perhaps, we will visit the hickory horned devil in a future bug of the week.
For more information on royal walnut moth and hickory horned devil including information regarding the rearing of silkworm caterpillars, please visit the following web sites. Thanks to Jeff and Linda for providing another great subject for this bug of the week.