Polyphemus: the Myth, The Moth, The Caterpillar (Antheraea polyphemus)



Staring into the face of the Polyphemus monster itself
Polyphemus moth caterpillar (Antheraea polyphemus)
Photo by Brad Sylvester. Copyright 2011. Do not copy.

 I had some old pictures of the polyphemus moth (Antheraea polyphemus) so I was quite pleased to find a polyphemus moth caterpillar as I went to check the mail. Because caterpillars and the moth or butterfly look so completely different,I particularly enjoy having images of both forms of an insect to post. It's absolutely fascinating to look at a caterpillar and see the similarities and differences between it and its adult form.

I also enjoy it when the first person to scientifically describe an insect is creative with the naming. This polyphemus moth caterpillar find is therefore particularly satisfying. Polyphemus, of course, is a name derived from Greek mythology. It is the name of the son of mythical Greek gods Poseidon and Thoosa. Students of the classics will recall that this was the same Polyphemus that was encountered by Odysseus (or Ulysses) in Homer's Odyssey. According to the legends Polyphemus was a cyclops, a one-eyed giant. The word cyclops is often thought o mean one eye, but it actually means round eye. Which brings us back to our moth.

In nature, eyes come in handy for two reasons: to find food or to spot predators before you become food. With many, many exceptions, those looking to spot predators have generally evolved to have very wide fields of vision so they can see predators coming from any direction. This means they often have eyes on the sides of their heads so they can see to the front and both sides all at once. Predators, on the other hand, generally have forward facing eyes that let them focus directly on their next meal.

• More Photos of the Polyphemus Moth and Caterpillar

As a predator then, if you see another animal that is staring back at you with two eyes both facing in your direction, there's a good chance that you're in for a fight. Thus, predators tend not to attack such creatures. When random spots and markings on a moth or butterfly's wings look like two big eyes staring back at an overhead attacker, overhead attackers think twice and leave those butterflies or moths alone. This means that the individuals with that sort of spot arrangement survive to reproduce and pass down their genes to offspring that look like their parents. Finally, the entire species may be descendants of those individuals whose spots just happened to look like eyes enough to fool its predators into thinking the moth or butterfly was staring right back at them with evil intent. Moth predators include toads, snakes, birds, bats and many small omnivorous mammals such as skunks and raccoons.

Polyphemus moth (Antheraea polyphemus)
Photo by Brad Sylvester. Copyright 2009. Do not copy.

The polyphemus moth is likely one such species. As you can see from the pictures here and in the linked slide show of photos, It has a distinct eye-spot on both the fore-wing and hind-wing. When the wings are swept back int he normal resting position, the eye-spots are staring straight up any would-be attacker. It is from these eye-spots that the polyphemus moth gets its name. Whether the discoverer named the moth after a cyclops because it had one-eye per wing, or because he knew that the word actually meant round eye and described the circular eye-spots of Antheraea polyphemus, I don't know.

Anyway, the polyphemus caterpillar shows no signs of the eye-spots that will as it undergoes metamorphosis in its cocoon. It does however, show signs that the rows of little black feet are different from the first six near its head. These first six feet, unlike the others, are pointed and brown. It is these that will become the adult moth's legs. The rest of the caterpillar's feet will be absorbed into the polyphemus moth's body in the cocoon.

Quick facts about the polyphemus moth (Antheraea polyphemus):

Diet: The caterpillar eats the leaves of many common deciduous trees such as beech, maple, birch and a number of others. Adults of this species do not eat at all.

Range: All across the United States and most of Canada.

When is it here? The polyphemus moth is here year round, overwintering in its cocoon.

Life Cycle: Adult polyphemus moths can be found from May to July in the North according to bugguide.net, however, I photographed the one shown above in mid-August. Caterpillars can be found from May until November. After that they will be in their cocoons for the winter. Since the adults don't eat at all, they exist only to mate and lay eggs. In warmer Southern states, two broods of Antheraea polyphemus may be raised each year.

Lifespan: The Polyphemus moth has a lifespan of approximately 12-13 months in the North.

Status: Common.

NOTES: The polyphemus moth caterpillar population is generally not dense enough to do any significant damage to forests or individual trees.

Greater Fritillary Butterflies (Speyeria spp.) and Nocturnal Caterpillars

Great Spangled Fritillary Butterfly (Speyeria cybele) --probably
Photo by Brad Sylvester. Copyright 2011. Do not copy.

I often see swallowtails and monarch butterflies (though not as many as I did years ago), but I had never really noticed the greater fritillaries. The greater fritillary genus (Speyeria) consists of about 15 species (give or take one depending upon which system is used) in North America, the largest of which measure out at just under a four inch wing-span. They belong to the same family, brushfooted butterflies (Nymphalidae) as the more well-known monarch, but receive much less attention.

In my yard, the greater fritillary butterflies prefer cone flowers, blazing stars (liatris spicata), and red clover. The caterpillars, however, are another matter altogether. According to the National Audubon Society Field Guide to North American Insects and Spiders, the great spangled fritillary caterpillar eats only the leaves of violets. furthermore, it will not be found on violets during the daytime as it leaves its food source to hide when it is light outside. At night, it returns to the violets and feeds. I looked for the caterpillars at night, but although there was damage to some of the violet leaves in my yard, I could not find them. They are fuzzy and black and have six rows of orange and red spikes.

Greater Fritillary Butterfly (Speyeria spp.) drinking nectar from a Cone Flower

The adult butterflies, however, don't try to hide. They happily flit about from flower to flower drinking nectar. It is difficult to identify some of the species of the greater fritillary genus (Speyeria spp.) because the visual differences are small. The one pictured on this blog entry and in the attached slide show is most likely a great spangled fritillary, but I can't be 100% sure of that identification so this is another one that gets an asterisk.

Quick facts about the Great Spangled Fritillary (Speyeria cybele):

Diet: Adult butterflies eat nectar. Caterpillars eat violet leaves.

Range: Although many species of greater fritillary butterfly have very specific ranges, the great spangled fritillary can be found over much of the United States except the southernmost part of the country.

When is it here? Unlike Monarch butterflies which migrate all the way to Mexico for the winter, greater fritillaries overwinter right here! The Audubon Guide says they can be found in flight (adult form) from May to October. This suggests that hard frost kills the butterfly itself, however, the caterpillars, says bugguide.net, after hatching in late summer or fall, don't eat and instead they overwinter as tiny caterpillars unchanged from from their hatching size until the following spring when the violets begin putting out new growth.

Lifespan: Not found, but likely about 13-15 months.

IUCN Redlist Status: Not listed. Common

NOTE: Butterflies will sometimes drink from hummingbird feeders, try the feeder kit shown below from Perky Pet one of the companies that helps sponsor this blog. At the time of this posting, they are a having a big sale on hummingbird feeders!

Double-lined Prominent Caterpillar Moth (Lochmaeus bilineata) - Or is it?

I’ve talked about identifying whether a particular insect is a butterfly or a moth, but what if it’s still a caterpillar? Often caterpillars have distinctive colors and patterns as well and can be identified that way. Some, however, like the Variable Oakleaf Caterpillar and the Double-lined Prominent Caterpillar, fall into the variable category, meaning that different individuals of the species may have substantially different coloration.

It’s not a minor variation either. It can be the difference between a caterpillar that is all green with narrow yellow stripes and a caterpillar that is green with a broad irregular reddish brown patch down the length of its back.  If I saw the two extremes of the Variable Oakleaf Caterpillar side by side, I would never have guessed that they were the same species.

That can be tricky if you are trying to identify a caterpillar by searching through photos. If you happen upon a photo of a color variant much different from your specimen, you may rule it out too early. That happened with me on the caterpillar pictured below.

Double-lined Prominent Caterpillar (Moth) - Lochmaeus bilineata (probably)
Photo by Brad Sylvester, copyright 2011, all rights reserved

At first, I thought that it could not be a Lochmaeus manteo (Variable Oakleaf Caterpillar), based on a few images I saw with a pronounced reddish saddle. Neither, however, could I find much else that was similar except the closely related Lochmaeus bilineata (Double-lined Prominent). By the way, Bugguide.net says the two may be indistinguishable in larval form, so technically, my specimen could be either species.  With some further searching and the use of a handy identification tool at Discover Life, I came back again to Lochmaeus bilineata and discovered some images of variants without the red marking on the back. These were nearly identical to my specimen, with the exception of two pairs of little red wart-like structures which should be present, but are not visible in my photos. Despite this, I am as certain as I can be that it is one of the two Lochmaeus species, and most probably Lochmaeus bilineatus or the Double-lined Prominent.

Clues to caterpillar identification

besides the color, pattern, presence of bristles, horns on its head or tail, and other distinguishing physical features, another clue to use to identify caterpillars is the type of food, usually leaves of some sort, which they eat. Some species of caterpillar are very picky about what they eat. In this case, both of the Lochmaeus caterpillars eat oak and other tree leaves. The Double-lined Prominent caterpillar that I found was eating a beech tree leaf, when I encountered it, although there is certainly plenty of oak on the property as well.

Another way to identify a caterpillar’s species is to see what it turns into after it undergoes metamorphosis. This, obviously, takes a little more time, and involves some risk to the caterpillar if you can’t keep it in a proper environment. If you aren’t sure what it eats, you shouldn’t even try to keep it captive until it pupates and forms a chrysalis or a cocoon. Even the chrysalis itself most likely requires the humidity and temperature to stay within a certain range to keep it viable. Ambient outdoor conditions for your region can be a good clue though.

If I had tried to keep the Double-lined Prominent caterpillar until it became a butterfly or moth, in this case, a moth. It would have formed a silken-thread cocoon and emerged as a pretty non-descript gray-patterned moth of small to medium size.

Quick facts about the Double-lined Prominent Caterpillar Moth (Lochmaeus bilineata)

Diet: Tree leaves: beech, oak, birch, elm, basswood, linden

Range: From New Mexico in the Southwest and Saskatchewan in the northwest eastward to the Atlantic Coast.

IUCN Redlist Status: Prevalent, not-listed

When they are here: Adult Double-lined Prominent moths can be found from June through August. I didn’t have a resource with good information on the larval life-cycle, but my BEST GUESS is that they overwinter in caterpillar form and form a cocoon when it gets warm in the spring, perhaps late April or early June based on the presence of the adult moth. The larva is certainly present in early-mid July, when I found this specimen.

Habitat: Deciduous woods