Caterpillars with pink and white stripes

2011 June 11

Sam and I found two of these while turning over pieces of dead log on June 14 of 2010 (almost exactly a year ago).

They looked big enough to be ready to pupate, so we tried rearing them in a jar. Unfortunately, they died (possibly because we didn’t know their correct foodplant) so we never did get to see the adult form.

They had the habits of a cutworm (hiding out underground during the day), so it seemed likely that they were some sort of owlet moth, but they were much more brightly colored than I’m accustomed to in cutworm caterpillars. Particularly the pale “racing stripes” running down their sides.

At first, I thought it might be a relative of the Striped Garden Caterpillar, genus Trichordestra. But, the Striped Garden Caterpillar has more stripes, and looks like it has a bigger head than the ones we found.

When I submitted it to BugGuide, John and Jane Balaban suggested that a better candidate would be something in the genus Nedra, which tend to be the same color, have the same number of stripes, and a similarly small head. The only Nedra species that BugGuide lists is the Gray Half-Spot, Nedra ramosula. It could be, I suppose, but the only foodplant listed for it is St. John’s Wort. The “common St. John’s Wort” is an introduced species that doesn’t look familar to me, and I don’t think it is actually growing anywhere near where we found these caterpillars. Of course, there are a number of other, native plants that are in the same genus as the common St. John’s Wort and commonly go by the same name, so it could be that the caterpillars were eating one of those. In any case, we evidently weren’t finding whatever it was when we tried rearing the caterpillars.

Incidentally, St. John’s Wort is a toxic plant (there are some problems with it poisoning livestock when it gets established in pastures), so it’s likely that the caterpillars that eat it are toxic too. This could be why these caterpillars are unusually colorful for a cutworm, it is likely to be warning coloration again. It sounds like St. John’s Wort contains an actual poison, not just a foul taste, so this could be pretty nasty if the caterpillar is actually retaining it in its tissues for defensive purposes.

Update: I have since found an adult of this species, the pictures are here.

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