Secondary sexual characters in centipedes are briefly discussed and it is suggested that the spines on the prefemora of the last pair of legs in some scolopendrids are used in specific discrimination prior to mating. The hypothesis is discussed with reference to Scolopendra spp. of the eastern Mediterranean, north-east Africa and Arabia. Where species of Scolopendra with virtually identical spinulation on the last legs are sympatric, a large size difference exists between them. It is suggested that in some genera where the prefemoral spines are absent, speciation may have been inhibited. In the genus Otostigmus where spines may be absent or spine patterns are very similar in a number of species other secondary sexual characters have developed.