Male black widows parasitize mate-searching effort of rivals to find females faster

Mate-searching success is a critical precursor to mating, but there is a dearth of research on traits and tactics that confer a competitive advantage in finding potential mates. Theory and available empirical evidence suggest that males locate mates using mate-attraction signals produced by receptive females (personal information) and avoid inadvertently-produced cues from rival males (social information) that indicate a female has likely already mated. Here we show that western black widow males use both kinds of information to find females efficiently, parasitizing the searching effort of rivals in a way that guarantees competition over mating after reaching a female’s web. This tactic may be adaptive because female receptivity is transient, and we show that (a) mate searching is risky (88% mortality) and (b) a strongly male-biased operational sex ratio (from 1.2:1 to >10:1) makes competition inevitable. Males with access to rivals’ silk trails moved at higher speeds than those wit...