Depending on the species, adult butterflies feed solitarily, in conspecific aggregations, in heterospecific aggregations, or in mixture of ways on blood, campfire ashes, dead earthworms and snakes, feces, fluids in soil, fresh and decaying fruit, fungus fluxes, honeydew, perspiration, putrefying matter including carrion, nectar, pollen, saliva, sodium salt, tree sap, urine, or a combination of these foods. Such aggregations comprise mostly or exclusively males. The principal goal of this study is to describe a huge feeding aggregation of seven butterfly species seen mostly on a 3.4-km-long, gravel-road route near the University of Kansas Field Station (KUFS). In addition, I provide information on butterflies’ aggregating elsewhere; the roadkill of thousands of adult butterflies; the frequency of an Asterocampa celtis melanic form; and some evidently previously unreported adult behaviors and foods. I examined the adult butterfly aggregation during the mostly sunny days of 5–8 June 2015. During each day, I walked along a different part of the route and counted and collected dead and maimed butterflies (both called “roadkills”) as needed to determine their species, total numbers, relative abundances, and sexes. I collected 204 male A. celtis roadkill specimens, without bias regarding their colorations, to examine their color patterns.
Asterocampa celtis was abundant and Celastrina neglecta, Enodia anthedon, Nymphalis antiopa, Pieris rapae, Polygonia comma, and Speyeria cybele were uncommon in the aggregation. Along the observation route, their density was up to scores per m2. The butterflies were also on sidewalks and stone walls. Besides being on the road, adult P. rapae aggregated on wet soil of a road bank. I found 710 roadkills, an average of 3.3 per m. This average times the total 3400-m-long aggregation, is 11,220 roadkills, a rough estimate of the total number during my observation period. I collected a sample of 204 roadkill A. celtis males, comprising 1 melanic and 203 non-melanic males, from roads. Asterocampa celtis population explosions may have occurred for centuries, perhaps millennia. An A. celtis population explosion in my study area has occurred annually from at least 1994 through 2015. Unlike butterflies in feeding aggregations along woodland streams or on road banks, in this aggregation, many butterflies were on roads and thousands of them were roadkills. From a conservation standpoint, one could save many lives of butterflies in road aggregations, including rare species, by placing traffic cones in key areas until the butterflies would disperse.