ABSTRACT I present evidence that antennal appendages contribute to male reproductive success in Eubranchipus serratus Forbes. Males will mate or clasp females in an attempt to mate repeatedly. However, receptive females typically reject a number of mating attempts before finally accepting a mate. Males with their antennal appendages removed succeeded in inseminating only 13 females out of 250 mating attempts while intact males were successful in 53 of 253 tries (x2 = 27.4, df = 1, P < 0.005). During unsuccessful mating attempts, receptive females were able to reject courting males by freeing themselves from the clasping males in less than 6 s in over 60% of cases regardless of whether the males had antennal appendages or not. The data suggest a mate recognition function for the antennal appendages.