ECHOES OF ULTRASONIC PULSES FROM FLYING MOTHS

¹ Department of Biology, Tufts University, Medford 55, Massachusetts

1. Moths of several species were mounted in stationary flight and the echoes of ultrasonic pulses were recorded simultaneously with flash photographs of the attitude assumed by the wings at the instant the pulse reached the insect.

2. The largest echo was produced by moths flying at the same altitude as the sound source when the potential course was roughly at right angles to the sound path and the wings were near to the top of the stroke. The difference between this maximum echo and that produced by the body and wings at other attitudes of the wing stroke was 30 decibels or more.

3. Moths flying at the same altitude as the sound source but on other courses produced echoes that fluctuated with wing position. However, the maximum was never as great as that registered on the 90° course.

4. Distortions in the shape of the echo are described and their causes are discussed. Scales on the wings or body of the moth do not appear to play an important anechoic role.

5. It is concluded that the plane surface of the wings returns the major portion of the echo. The significance of this is discussed in relation to the problems of detection and evasion encountered under natural conditions by bats and flying moths.