This male specimen belongs clearly to the genus Dolichopus with 317 species in North America north of Mexico (see Pollet et al., 2004; Brooks et al., 2005 - on-line checklist). The enlarged fore tarsus is an example of Male Secondary Sexual Characters that are used by the male sexe during courtship (to attract, convince and seduce female specimens).

This is probably a species of Dolichopus. In that genus are umerous species with morphological adaptations to their legs. Enlargement of one or more tarsal segment (like here) is one of those possible adaptations. A similar adaptation, but not so pronounced, is found in the European D. melanopus.

Paul

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