COMMUNICATION BY STRIDULATORY SIGNALS IN LEAF CUTTING ANTS .2. PRODUCTION AND CHARACTERISTICS OF SIGNALS

1. Structure and function of the stridulatory apparatus in leaf cutting ants (especially Atta cephalotes) are described. The posterior rim of the postpetiolar tergite acts as a scraper, an area of parallel ridges at the anterior end of the first tergite of the gaster is the file. 2. The temporal pattern of stridulatory sound is analyzed in oszillograms. The ant produces trains of short transient clicks by pulling the file forward beneath the scraper; each impact of the scraper against a ridge of the file gives a click. External factors (temperature, mechanical stimuli) and central mechanisms, localized in the petiolar ganglion, determine the stridulation pattern. 3. The intensity spectrum of airborne stridulatory sound extends from the upper audible range far into the ultrasonic with a maximum between 20 and 60 kHz. At a distance of 0.5 cm from a soldier ant of Atta cephalotes, a sound pressure level of 74 dB re 0.0002 μbar has been measured. 4. The intensity spectrum of soil conducted stridulation sound does not contain frequencies above 6 to 8 kHz; an intensity maximum is concentrated between 1 and 3 (up to 5) kHz. A soldier ant, covered by 1 cm of sand, can produce a peak-to-peak signal amplitude of 18 cm/sec2 at the surface. Soil conducted stridulatory sound is attenuated 6 dB/cm. 5. Physical aspects of sound production by a stridulating ant are discussed. The vibration spectrum arising from the movement of the scraper over the file is derived. It is concluded that the spectrum of a periodic sawtooth vibration together with the spectrum of short impacts are basic elements of stridulatory sound production. Taking into account the conditions of sound emittance in air and soil the experimentally determined spectra of stridulation signals can be explained. Considering a soldier ant as a simple sound-source, the total power radiated is found to be 1·10-1 to 2·10-1 erg/sec. © 1968 Springer-Verlag.