Thanks for your efforts -- and thanks to Janice, too. Jo and I will stay tuned.

I've searched through my data base and found a white, hairy, immature Spilosoma virginica, which turned reddish brown when it matured. White hairy caterpillars are hard to ID positively, unless you rear them out.

Below is a quote from Andrew Williams regarding your white hairy caterpillar and caterpillars on Milkweed in general. Andrew is president of the Wisconsin Entomological Society, an honorary fellow in the UW-Entomology Dept. and founder and president of Prairie Biotic Research. He does field work all over Wisconsin, with food plant specificity and parasitoidism being of great interest to him.

“There is a report from 1920 of C. oregonensis ‘bred from Asclepias sp.’ in Iowa. I have not found C. oregonensis using any species in Asclepias. Cycnia tenera has been reported to use various species in Asclepias, but some of these reports are second hand and perhaps refer to an erroneous report in which this caterpillar was confused by that author with C. inopinatus. I haven't yet sorted this all out. I myself have found C. tenera larvae, even small larvae, feeding on Asclepias syriaca, 4 larvae on 2 occasions, both of which times the milkweed grew in immediate proximity to the Apocynum on which the moth probably laid her eggs. Errant larvae can develop on A. syriaca, at least. I haven't yet found C. tenera larvae on other species of Asclepias. I don't think this photo is of C. tenera (body hairs too short relative to head and tail-end hairs, color seems to vary on one animal, color too pale for a last instar, which this appears to be by its size). This photo could well be C. oregonensis. There is a reliable report of another "milkweed feeder" switching from Apocynum to Asclepias tuberosa -- Saucrobotys futilalis (Pyralidae) has been reported to make this switch. Indeed, because so many 'milkweed specialists' feed on both Asclepias spp. and Apocynum spp., habitually or occasionally, I include all these plants and their composite fauna in my study of isconsin's ‘milkweed fauna.’ Then again, this photo might be a younger instar of Spilosoma virginica, which has very wide feeding interests. Though I have not yet found S. virginica feeding on A. tuberosa, I have found and reared out these larvae on five other Asclepias species. You've heard me say it before, Janice, but a photograph is often only tentative. The discoverer had a great opportunity to rear out that caterpillar and tell us the truth. As it is, we are left tantalyzed, guessing. If the photographer did rear the caterpillar out, I'd like to contact the photographer, regardless of what state he/she may live in.”

Unfortunately, we've missed the opportunity to rear the caterpillars out. We'll add this information to our file for this photo and hope we get another chance -- not likely, but you never know.

Thanks to everyone.