Mole Cricket Audition
Some animals improve audition when it matters most.
Mole crickets are large burrowing insects that live underground in extensive tunnel systems. Mole crickets live in every continent except Antarctica, and are commonly considered pests, except in East Asia, where they are considered a tasty fried snack.
A male mole cricket rapidly rubs his forewings together to sing seductive songs to attract a female. But first he builds a concert hall: sculpting an acoustically excellent horn in a burrow which sonically enhances and amplifies his chirps.
Having optimized for audition, he auditions. The male performs with his head at the front of the horn, getting the best possible sound.
Grylloptalpa gryllotalpa is a mole cricket with small wings and shallow teeth on its file. It chirps a quiet song at ~1,600 Hz. Another species, G. vinae, loudly sings at 3,500 Hz with its large wings and deep-toothed file. (Note that higher pitch carries a shorter distance through vegetation, and so may be compensated via volume.)
G. vinae builds a double exponential horn with smooth walls. The 2nd bulb in the concert hall acts as a resistive load for the vibrating wings, concentrating the sound to a disc-shaped patch just above the burrow.
The lower-pitched G. gryllotalpa builds a single-chamber larger cavity that effectively amplifies at that frequency.
Hence, the burrow, wing structure, and singing of male mole crickets are all precisely co-adapted to entice females of their respective species.
