In warm conditions the male calling song, heard most often in the evening and at night, is a dense echeme of diplosyllables followed immediately by a characteristic 'click'. The echeme usually lasts between 1s and 3s, but at very high temperatrures can be as short as 0.5s. The sylllables are repeated at the rate of about 30-50/s,ally accelerating slightly and becoming louder duringthe course of the echeme. In the songs studied the number of syllables in one echeme varied from 20 to 90. The echemes are sometimes repeated at irregular intervals, but can be repeated more regularly for short periods.
Oscillographic analysis shows that there are opening and closing hemisyllables, sometimes of equal loudness and duration (especially towards the end of the echeme), but more often (at least in the earlier part of the echeme) the opening hemisyllables are slightly louder and longer than the closing ones. Each diplosyllable usually lasts 20-30ms, but in hot conditions can be a little shorter than this. The main echeme usually ends in a slightly prolonged closing hemisyllable; there is then a very brioef interval (about 20-80ms) followed by a further, 'click-like', closing hemisyllable, usually lasting 15-50ms. Heller (1998) has shown that the fore wings are vibrated in a relatively open position during the main echeme and that the final 'click'; is produced when they return to a closed position.
Willemse (1979: 136), referring to AcrometopaI in general, gives the duration of an echeme as 5-10ms. Our own experience suggests that A. servillea would produce such long echemes only in very cool conditions.
- . The Songs of the Grasshoppers and Crickets of Western Europe. Colchester, Essex: Harley Books; 1998.