Fig. 3. Six different experimental settings were ensonified with a probe signal, and the echoes were recorded. Representative recordings are plotted as oscillogram (above) and spectrogram (below) representations. In all recordings, the outgoing signal and its second harmonic can be seen as recorded by the microphone positioned 5.6 cm laterally to the speaker. These are distorted because of the frequency-specific directionality and lateral position of the speaker and microphone. A good recording of the outgoing signal is shown in Fig. 2D. We ensonified the nylon threads in the air in the absence of a mealworm (A) and in the presence of a mealworm (B), of the linoleum screen in the absence of a mealworm (C) and in the presence of a mealworm (D) and of the clutter screen in the absence of a mealworm (E) and in the presence of a mealworm (F). In all the recordings depicted here, the mealworm was positioned at approximately 90° to the impinging sound. In air and on the clutter screen, the mealworm reflected back a good copy of the ensonification signal (B,D), whereas the echo from the clutter screen did not differ when a mealworm was absent (E) or present (F). Threads in air did not reflect any conspicuous echo (A), and the recording was identical to a recording of the noise floor of our apparatus. The level of clutter echoes reflected off the linoleum screen (C) was low in comparison with that reflected off the clutter screen (E). The latter yielded a smeared echo that extended over a wide time period. The linoleum screen reflected a strong ‘ground echo’ only from immediately below the ‘artificial bat’.
