Record size Imperial moth, July 19, 2012!!

This unusually large Imperial Moth visited my mercury vapor light overnight last night, and the first thing I noticed about her is her unusually big size. I have been collecting, and dealing with butterflies and moths since I was 10 years old in July of 1968, and in those ensuing years, I have had numerous dealings with Imperials, as well as all the other indigenous species of the giant silk moth family in Pennsylvania, such as the Cecropia, Luna, and Polyphemus moths. I have never seen an Imperial moth in this gargantuan size before in my whole life. The average live unmounted. wingspan of these moths is usually around 5" to 5-1/2". This one has a wingspan of 6-9/16"! Rounds down to 6-1/2". That is about the average wingspan of a female Cecropia (Robin) moth, the largest indigenous giant silk moth in North America. Cecropias can get as big as 7-3/8" in wingspan, so they still hold the record in my book. But this particular Imperial gives the Cecropia a run for its money. In a way of comparison, the Monarch Butterfly has a wingspan of about 4". Maximum wingspan is measured when the wings are in maximum natural wingspan position, which is usually the position the wings are in when the insect is in flight, as the image immediately below shows.

My wife calls this moth, the "Scrambled Egg Moth" as its coloration looks like that to her. When each of my family members saw it they all went "Oh, My Gosh!!". They all have seen the different species that I have raised, captured, and bred over the years, but they also have never seen an Imperial this big before.

The caterpillars of this moth feed mainly on the leaves of sassafras, pine, walnut, and Norway (hard) maple.
The adults do not feed. Their job in life when they reach this stage is reproduction, then after that, they die. 

UPDATE

Here is the mounted specimen. Since this moth is so unusually large, I felt that she should be preserved for prosperity. But before she was preserved, she laid a few fertilized eggs, which have since hatched. I am now in the process of raising 13 caterpillars that have hatched from them. I will update this blog post as the caterpillars grow, which takes from what I read on the internet, takes about 2 months, or around 60 days to reach maturity. They will then stop feeding, and burrow underground to pupate. That should happen sometime in mid to late September.

Below, are the first images of this moth's offspring. These caterpillars are about 4 days out of their eggs, in the first "instar", and are in real life about 1/2" long. An "instar" is a period of growth every caterpillar goes through, which ends with the caterpillar shedding it's skin like a snake, so it can continue to grow bigger. The skin will only stretch so much before it gets too small to handle the caterpillar's growth. Each time it sheds it's skin, it is then able to eat and grow some more before they shed again. Most butterfly and moth caterpillars do this 5 times. The last time is when they change into a pupa,or in the case of butterflies, it turns into a chrysalis. Most moth caterpillars spin cocoons before they shed that final caterpillar skin inside that cocoon, away from prying eyes. With the Imperial moth, though, it's caterpillars, when they are full grown, burrow a few inches underground before it turns into a brown pupa, in it's hollowed out subterranean chamber.

The Imperial caterpillars are growing very fast. I am feeding them on Norway Maple, which is a hard maple.

The images below are greatly magnified as these guys, like I said are only about 1/2" long, right now. They are right near the end of their first instar of growth.

UPDATE 8/23/2012   (Edited and added 9/1/2012)

The image below is of  the offspring of that big Imperial Moth that I caught last month, on July 19th. I started with 13 caterpillars. 8 are left, due to circumstances beyond my control. I am raising them in a screened 6 gallon bucket pail with small Norway Maple branches stuck in a baby food jar in the bottom of the bucket, with water in the jar that has a hole in the lid to accept the cut branches, but it keeps the caterpillars from crawling down into the jar, and drowning. This keeps the leaves fresh for a lot longer than just throwing leaves loosely in the bottom of the container for the caterpillars.  These two guys are in their fourth "instar", about mid term in their eating and growth life. I am rearing them on Norway Maple leaves. Right now they are about the size of a tobacco hornworm, another caterpillar that looks similar to the one that Mark posted, but a tad bigger. At  the end of this fourth instar, the Imperial larvae will shed their skins, and will enter the fifth and final instar of growth before they burrow underground to pupate to overwinter,there. When these caterpillars are full grown, they will be over 4 inches long, and fatter than my index finger! Yes, they get that big!!

Jim.