Digger wasp against crickets. II. An airborne signal produced by a running predator

Abstract

Females of the digger wasp Liris niger Fabr. hunt crickets to provide food for their offspring by running with high velocity on the ground (>20–50 cm/s). Crickets are able to detect the running wasps by the air particle movement generated by the predator. We measured signals produced by running wasps using a microphone sensitive to air particle velocity. The wasps generated single air puffs with peak air particle velocities of 1–2 cm/s measured close to the running wasp. We measured frequency spectra of the signals containing only components below 50 Hz, with increasing intensities towards lower frequencies, especially below 10 Hz. We measured the air particle movement generated by artificially moved wasps, crickets or a styrofoam dummy of similar size to investigate the effect of velocity and shape of the moving object upon the composition of the signal. The velocity of movement appeared to be important for the intensity and frequency composition of the air particle movement. The shape of the moved body had an influence on the intensity but only little effect on the frequency spectrum. Measurements with a thermistor anemometer showed that a moving object caused air currents lasting longer than 100 ms after passing or approaching the probe. The air particle movements generated by hunting wasps are entirely sufficient with respect to intensity and frequency range to be registered by the filiform hair sensilla upon the cerci of crickets.