In what is either a remarkable coincidence or evidence of an expanding genista broom moth population, another co-worker waltzed in about an hour later with yet another of these caterpillars. He lives 40 or 50 miles north of the other caterpillar collector, in Morrow County. His caterpillar is the other specimen in the photo. After determining that my two colleagues weren't pranking me, I set about learning a bit about this moth and its larvae.
Photo: Wikimedia Commons, photographer unattributed
Several species of Baptisia, or indigos, are commonly sold and planted in gardens and yardscapes, including this wild blue indigo, Baptisia australis. In Ohio, it is primarily a species of gravelly river bottoms, and now is known but from one site in the wild and is listed as endangered. We've got two other native indigos in our flora: white false indigo, B. alba (white or creamy flowers), and yellow false indigo, B. tinctoria (yellow flowers). While both of these species are rather rare in the wild, they both are sold at least sparingly in the nursery trade. The genista broom moth caterpillar could turn up on any of them, as well as other pea family plants in the genera Genista, Lupinus, Sophora and perhaps others.
I conferred with Dr. David Wagner about this species, and he tells me it does seem to be on the move and has turned up recently in new east coast sites (the species is principally a westerner). The caterpillars apparently can assimilate toxic alkaloids from their host plants and sequester them, thus they are chemically well protected. Thus, their daytime habits as most birds won't fool with them.
In spite of Internet maps showing dots in Ohio, there apparently is no validated record of genista broom moth for the state, or at least of larval infestations. This species may be an up and comer in our neck of the woods, and it bears watching for. If it increases and jumps from the garden Baptisias into the small, local and widely scattered native Baptisia stands, there could be trouble.
If you've seen this caterpillar, let me know, and ideally take a photo and send that too. The adult moths are rather plain and would be far more likely to go unnoticed than the conspicuous caterpillars.