In mid-Atlantic estuaries, 3 species of fiddler crabs (Uca pugilator, U. pugnax and U. minax) co-occur, with their adults occupying different habitat types separated by salinity and sediment size. There is evidence that selective settlement is responsible for this separation, but the mechanism for selection is unknown. We examined the effect of chemical cues from adult fiddler crabs on the metamorphosis of field-caught fiddler crab megalopae. Previous research found that cues from adult conspecifics accelerate metamorphosis of lab-reared megalopae. We tested the hypothesis that chemical cues from conspecifics would also stimulate molting in field-caught fiddler crab megalopae. Individual megalopae were held in estuarine water (control) or water in which adult crabs had been incubated; the time each megalopa took to metamorphose was recorded. Over a 10 d incubation period, 40 to 60% of the test megalopae molted into juveniles. Only U. pugilator accelerated molting but did so in water that contained any adult cue, indicating that this species may not be very selective. A significantly higher proportion of megalopae of all 3 species molted in conspecific water than in estuarine water or water containing odors of other species. This indicates that chemical cues from conspecific adults are important in regulating molting and that the stimulation of molting to occur may be as important as acceleration of the timing of molting. This stimulation, in conjunction with a behavioral change to terminate flood-Tide transport, is likely important in selective settlement of fiddler crab megalopae.