Discrimination of conspecifics' chemicals may allow Spanish terrapins to find better partners and avoid competitors

► Turtles discriminate individual traits of conspecifics based on chemical cues alone. ► Male turtles prefer water with chemicals of females with greater immune responses. ► Females prefer water pools with odours of larger males. ► Males avoid chemicals of heavier males and prefer chemicals of smaller males. ► Chemosensory assessment may optimize mate searching and avoid male competition.