The evocative song of the cicada is one of nature's great sounds. These small grasshopper-like insects make a noise that is atmospheric, enigmatic and very, very loud.
Males generate the sound by repeatedly flexing drum-like organs in their abdomen, which is largely hollow, intensifing the sound. Larger males produce louder calls, and so have a greater chance of attracting a mate.
But is it the loudest sound produced by any insect? John Petti, formerly of the University of Florida, decided to find out. He searched published research and asked fellow entomologists for suggestions as to what the loudest known insect might be.
Various candidates from the Orthoptera order (crickets and grasshoppers) were proposed, including the large field cricket from Malaysia, bladder grasshopper, wrangler grasshopper and European mole cricket. The last of these was found to be the loudest at 96 decibels at a distance of 50cm away.
Yet several species of cicada have been found to be louder. The loudest of all was an alarm call of 108.9 decibels by a Tibicen walkeri, one of two types of Walker’s cicadas that lives in North America.
However Petti ruled the title should be awarded for the loudest mean volume. T. walkeri’s was loud at 105.9 decibels at a distance of 50cm, but not as loud as the 106.7 decibels generated by Brevisana brevis, an African cicada.
While they can seem similar to human ears, the sounds male cicadas make to attract females and to express alarm are different. One study found that the alarm call of the desert cicada (Diceroprocta apache), just 0.5 decibels quieter than the record holder, reduced the effectiveness of attacks by its predator the southern grasshopper mouse.
B. brevis may not hold the title indefinitely however. In a study carried out in 1995, entomologists measured the volumes of calling songs made by 30 cicada species and the alarm calls of 59 species – all in North America. They concluded the noise level they were capable of achieving correlated with their body mass.
While B. brevis weighs 0.3g when dried out, the huge Empress cicada of southeast Asia, which has a wingspan of 18-20cm, weighs in at 2g. Anecdotal evidence suggests it is extremely loud, and it may only be the lack of any known scientific attempt to measure just how loud that is preventing the Empress from claiming the record.