Evidence for use of chemical cues by male horseshoe crabs when locating nesting females (Limulus polyphemus)

Horseshoe crabs come ashore in attached pairs during spring high tides to m ate and nest on beaches of the Atlantic and Gulf coasts. Unattached males a lso come ashore and crowd around the nesting pairs as satellites and engage in sperm competition with the attached male. Females with no satellites an d females with large numbers of satellites nest next to one another on the same tide. When females are removed and replaced by a cement model, satelli te males continue to be attracted to the same location. Models over sites w here females with many satellites had nested are more attractive to males t han sites from which a female with no satellites had been removed or a site where no crab had been nesting recently. A second experiment demonstrated that males are responding to chemical cues. A sponge filled with seawater t aken from below a female with many satellites and placed under a model fema le was more attractive to males than a sponge filled with seawater. This is the first demonstration that horseshoe crabs use chemical cues, in additio n to visual cues, to locate mates.