Pick-up lines: cues used by male crab spiders to find reproductive females

The low population density of the crab spider Misumena vatia and the high percentage of gravid adult females begs the question, how do adult males find reproductive females' We explored one of the potential mate-locating tactics of adult males, their line-following behavior. M. vatia do not build webs; however, they do lay down silken lines during their movements. In both the field and the laboratory, adult males (but not juvenile males) regularly followed lines of other individuals, as well as their own, sometimes multiple times. However, they did not distinguish the direction in which lines were laid, and they even followed Lines of other species. Males responded mechanically to these lines, but not chemically. They followed lines of penultimate and adult virgin females, as well as new and old lines, with similar high frequency. Neither washing the lines with water nor washing them with acetone (to remove possible water-soluble or organically soluble pheromones) affected their choice of lines. Due to the low activity of females, their lines may be several days old, over which time arty possible chemical information would likely dissipate. Therefore, pheromones seem unlikely to aid males searching for unmated adult females. Nevertheless, even searching males that follow Lines largely indiscriminately should derive a benefit because concentrations of Lines could denote the presence of females and thereby maximize numbers of females encountered.