Friday, 25 October 2013

The Recent Cacophony

The cricket producing this intensive sound was about 25 cm (10 inches) from the microphone. It is Cephalogryllus tau Alexander & Otte, a member of the Gryllidae; subfamily Gryllinae. The sound is ear-piercing, even to these old ears when up close. The crickets seemed randomly spaced but fairly close together. The background sounds are largely of this species. The beeps towards the end of the recording are of a small frog.

The antennae are extended from the burrow and wave back and forth. The short-winged cricket is adapted for a tight burrow. Long wings would require a larger burrow and that might lead to a greater array of predators like bandicoots and geckos.

During the day, the burrows are closed by the crickets and are reopened after dark if the night is suitably humid.

Why do the crickets sing? Well it is widely agreed that crickets sing for several reasons. The most common reason is the sounds are specifically designed to attract mates. Males produce the call. However, territorial or aggressive calls have been observed in many crickets. Since C. tau is a relatively recent discovery, nothing is known of its biology other than it lives in burrows. In this genus the females are very short-winged, the tegmina only about 1/3 the length of the pronotum. They produce no sounds. Presumably, the females wander about on the surface of the ground seeking singing mates. However, no females were observed on the evening the recording was made.

Some mention should be made of how crickets produce song. Almost all crickets and katydids produce sound by rubbing their wings together and that is almost the exclusive domain of males. In katydids it is usually the left wing (tegmen) that is rubbed over the right. In crickets, for some reason, it is the right that is rubbed over the left. Sounds produced in this way are called stridulations. This is called the file and scraper method. The analogy is similar to running your thumbnail across the teeth of a comb.

The loud sound produced by G. tau is surprising considering the short, stumpy size of the wings themselves. 

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