The Backyard Arthropod Project

Back on March 30, there was a rare sunny, not-quite-freezing day, and we took the opportunity to take a walk down the road. On the shoulder of the road, right next to our yard, we spotted this caterpillar:

It had obviously overwintered as a caterpillar, it certainly hadn’t gotten that big in the approximately 3 above-freezing days that we’d had at that point. It looked it, too - a bit weathered, kind of scruffy, not moving very fast. It’s certainly a caterpillar of some type of tiger moth, in the family Arctiidae. These are pretty large moths that have fuzzy caterpillars, like the well-known wooly bear caterpillar. This one isn’t a wooly bear, but I think it is the caterpillar of one of the moths in the tribe Arctiiini. BugGuide is kind of short of caterpillar pictures here, but from Wagner’s book I’m inclined to think it’s either the Great Tiger Moth, Arctia caja, or the St. Lawrence Tiger Moth, Platarctia parthenos. Unfortunately Wagner’s picture of the St. Lawrence Tiger Moth caterpillar doesn’t look quite right either, but he does say that it is more uniformly dark than the Great Tiger Moth, with brown spiracles. I can’t see the breathing spiracles at all, so they must be brown:

The head is black, too, instead of brown

And the setae (hairs) come out of a kind of warty tuft instead of being spread uniformly over the body

So, on balance, I’m leaning towards the St. Lawrence Tiger Moth, but in either case, the caterpillars are pretty similar as far as habits. They overwinter as partially-grown caterpillars, and then eat a bit more in the spring before pupating and emerging as adult moths. They aren’t very fussy about their food, eating grass, legumes, and pretty much any other low-growing plants that are available. Wagner refers to them as the “musk oxen” of caterpillars, because they are big, hairy, and shrug off the cold. They are also rather long-lived, the St. Lawrence Tiger Moth can take two years to get to adulthood, overwintering twice.

Other articles related to this topic:

• Ctenucha virginica caterpillar
• Codling Moth Caterpillar (Worm from an Apple)
• Cutworms
• Black-Etched Prominent Caterpillar
• Variegated Fritillary Caterpillar