Buckeye butterflies seemed even more numerous on campus yesterday than they were last week (see “Having a spectacular year” below). These two even stopped to mate alongside College Drive while on their way southbound.

I am not sure which is the female. The different patterns of red on their under-wings is not a sexual difference, but instead the variation in color that both sexes of Junonia coenia show in fall. If the female’s eggs have been successfully fertilized here, she will have to carry them over the Delaware Bay and southward — or they won’t survive. Buckeyes cannot withstand NJ winters. Adults must migrate out of the state each fall to give their offspring a chance to grow up as caterpillars somewhere in the southern U.S. and finally to reach adulthood to breed themselves. That generation are the parents that will send the next set of buckeyes — the grandchildren of the College Drive pair — back north to NJ next spring.

At least, that’s how the story is understood at the moment. In truth, the migration of this butterfly is a field problem waiting a young scientist’s fascination — or, better probably, that of a team of young scientists. Despite the species’ abundance and the eye-catching autumn spectacle, the flights have not yet been studied in detail, it seems. Working out the general outline of the monarchs’ migration to Mexico required several decades. Discovering the basics of buckeye flights might prove just as much a challenge.