~George Santayana

I awoke early this morning, too early. What to do? I looked out and saw a moth at the lighted kitchen window. My brain drifts to my recent sightings of moths and their seemingly endless variety. Perhaps I will learn a new one today. I know something about some groups of moths, especially their caterpillars, but have never taken the time to get to know many of the adults. So, I sat down and looked at some moth images taken last week when I left the porch light on all night in hopes of attracting a few to the screen. Some of them stood out for their odd posture – they were perched with their abdomens curved up over their backs. I have seen this on many occasions, but never took the time to try to identify them. I have always assumed this has something to do with releasing pheromones for mate attraction. But, In researching this online, there doesn’t seem to be a clear explanation for this behavior. I was, however, able to learn a bit about the identity of my odd visitors.

Slug Moths often perch with their butts pointed skyward – this rather plain one is most likely a Red-crossed Button Slug Moth, Tortricidia pallida (click photo to enlarge)

This “moth mooning” is common in several families of moths, but one, in particular, seems to make it a habit – the Slug Caterpillar Moths (or just Slug Moths), Family Limacodidae.

Nason’s Slug larva

The group is named for their larvae, the so-called slug caterpillars. They are a fascinating and bizarre bunch which lack the usual paired prolegs found on most caterpillars, and, instead, move about in a slug-like gliding motion. They are one of my favorite groups of insects, as many of the larvae have odd shapes, colors, and armaments (several species have urticating spines which can inflict a painful “sting” if handled carelessly). But, I know relatively little about the adult moths of this group, so I dove into a few online resources this morning to try to figure them out.

Shagreened Slug Moth, Apoda biguttata

The North American Moth Photographer’s Group has a set of color plates that let beginners “walk through the moth families” as a way to get started on moth identification. You can scroll through the plates until you find a moth that resembles the one you have and then click on it for more species. I did that and quickly found that these moths belonged to the Slug Moth family. I then turned to my favorite online invertebrate resource, Bug Guide, and began to scroll through the images of Limacodid moths. I found what I think were all of the species resting on my screens that morning. The oddball name winner was the Shagreened Slug Moth. Shagreen is a name for untanned leather and must refer to the rough texture and color of this little beauty. Another common name is the Two-spotted Apoda. The genus name, Apoda, means lacking feet (the slug-like larvae); biguttata means two spots.

Yellow-shouldered Slug Moth, Lithacodes fasciola

I quickly identified the other species and then noticed that not all of the online images had these moths in that pointy-butt pose. So, I took a look at one moth I had found that seemded similar in size and shape, but that was apparently more demure and kept its derriere covered on my screen.

Inverted Y Slug Moth, Apoda Y-iversum

If I identified it correctly, it is another one with a strange name – the Inverted Y Slug Moth. It turns out that most of these species may rest with their abdomen tip curved up or tucked beneath the wings. The exposed abdomen tip posture may be an adaptation to avoid detection by predators that use sight to find food. The odd posture makes for an odd outline that may resemble a broken twig or piece of vegetation more than a moth. Whatever the reason, it did help me get started on a quest to learn more about the night-time visitors at my windows. Now that I know a little more about them, I look forward to seeing them and their kin on a more regular basis.