This spring, as I was exploring the woods of Nashville, Tennessee amid the overbearing din of periodical cicadas (the thirteen-year varieties), I found some striking caterpillars feeding under webbing on a plant that was new to me, but seemed vaguely waterleaf-ish:
After conferring with some friends who are more familiar with non-New England plants, I determined that the plant was Phacelia bipinnatifida, a.k.a. fernleaf phacelia, which is in fact in the waterleaf family (Hydrophyllaceae), though that apparently is now considered a subfamily of the forget-me-not family (Boraginaceae). But even knowing the host plant, I was unable to find a match for these distinctive caterpillars in books or online.
Today, 6½ months later, I was scanning through Braun‘s 1925 paper, “Some Undescribed Lepidoptera and Notes on Life Histories” (Transactions of the American Entomological Society 51:13-17), in the process of tracking down descriptions of some little-known leafminers’ mines, when I came across an entry for Ethmia zelleriella (Elachistidae), which began: “The larvae were found feeding exposed on the upper surface of leaves of Phacelia bipinnatifida, near Cincinnati, August 15.” This of course caught my attention, and I scrolled down to see: “The full grown larva is a brightly colored and beautiful creature. The ground color is chrome yellow, marked with velvety black spots and irregular longitudinal black or bluish black stripes and bands. Each tubercle area is black . . . and there is, in addition, a longitudinal dorsal series of black spots . . .” and she went on to describe every marking in perfect detail, in addition to the habit of feeding under webbing, leaving no doubt that these were the caterpillars she was describing.
It turns out that if I had just searched the Database of the World’s Lepidopteran Hostplants, I would have found that Ethmia zelleriella is the only caterpillar known to feed on Phacelia bipinnatifida (and, as it happens, P. bipinnatifida is the only known host plant for E. zelleriella). A Google image search for Ethmia zelleriella yields no photos of these caterpillars, though, so even if I had done that I wouldn’t have been sure until I’d found this article. There are plenty of shots of the adult moth, though, and it’s a nice one.
So there you have it, possibly the first (identified) photograph of an Ethmia zelleriella caterpillar.