Among grasshoppers the Saltatoria emit "complex and highly specific songs." The hind legs are rubbed against the wings and the sounds produced are perceived by tympanal organs on the legs. Such activity is a clear mating display. Above a certain temperature the males of the species may sing spontaneously, sounding a number of notes followed by a pause. A receptive female answers with a softer call. The male and female then call alternately, the male now with a newly modified song. In threat displays two males may sing at each other. Perdeck has shown ("The Isolating Value of Specific Song Patterns in Two Sibling Species of Grasshoppers - Chorthippus brunneus Thumb and C. biggutulus L." "Behaviour", Vol. 12, pp. 1-75) that grasshopper songs are sexually stimulating to both sexes. In fact females get so excited that they even try to mate with silent males of the wrong species; and males speed up their locomotion and their efforts to copulate.