Attempted copulation of two Calopteryx maculata (P. de Beauv.) females by a Stylogomphus albistylus (Hag.) male (Zygoptera: Calopterygidae: Anisoptera: Gomphidae)

S. albistylus is present at low densities on the Palmer River in Rehobolh (Bristol Co.), Massachusetts where we have been engaged in a study of C. maculata. Male S. albistylus perch on the muddy banks while females apparently perch away from the stream. The operational sex ratio appears to be highly male-biased; we have observed females in copula only. The two species are similar in size, but Calopteryx is far more numerous than Stylogomphus at the study site. On 7 July 1986. we observed an S. albistylus male fly from his perch toward a flying C. maculata female. He knocked the female into the stream and then perched on her head while attempting to grasp it with his anal appendages. We were able to observe this behavior quite closely since one of us was standing in the stream at the time. The interaction was clearly an attempt at tandem formation, not predation. The male was unsuccessful in his attempt to grasp the female and returned to his perch. A few minutes later, an , S. albistylus male, presumably the same one. attempted to grasp another C. maculata female in the same manner and again failed.