Male Amblyomma americanum (Linnaeus), A. maculatum Koch, and Dermacentor variabilis (Say) display behavioral responses to a chemical substance (pheromone) in extracts of females of each of the 3 species which are characteristic of those exhibited in mating. It is believed the function of the compound is similar to that of sex pheromones in other arthropods. The males must reach a certain state of maturity, which is initiated by feeding, before they will respond. Unfed as well as fed females contain the pheromone. Chemical properties of the active substance indicate it is a weak acid, possibly a phenol.