Daniel Wright of Green Island School asks :-

Why do insects make noises?

Anthony Harris, an entomologist at the Otago Museum, responded.

Some noises result from an insect's normal functions, such as the whirr of its wings in flight, but very often insects' noises are produced for communication by specialised structures.

Some insects make sounds to attract a mate (e.g., wetas, cicadas, crickets, booklice); to prevent damaging a sibling (e.g., wood-boring beetle larvae from running into each other); or for defence (e.g., a ground weta in its defensive threat posture raises its barbed hind legs high into the air then stridulates loudly as the legs are kicked downwards - which might scare a predator.) A longhorn beetle squeaks when held, so the attacker may become alarmed and drop it.

Many insects communicate with vibrational signals that can sometimes be heard by humans. The insects produce sound in different ways.

WING BEAT. Many small flies attract mates by beating their wings at a certain frequency.

PERCUSSION. This refers to vibration produced by the impact of some part of the body against the substrate or by striking another part of its own body. Booklice, although only 2 mm long, tap their abdomen on the substrate causing a tiny sound, like the ticking of an old fashioned watch, audible in many New Zealand homes. If you sit during the evening in a quiet room near a book case in an older house, you will often hear it.

STRIDULATION. This refers to vibration made by moving a scraper on one part of the body against a file on another. Male crickets have a file on the second cubital vain of the forewing, and a scraper near the wing margin. The wings are partially raised, then opened and closed so that the scraper of one forewing rasps on the file of the other forewing. The four species of small, black or dark brown native crickets sing during the day with a very high sound audible in grassy places throughout the country.

TIMBAL MECHANISM. A timbal consists of thin cuticle surrounded by rigid frames. Vibrations result when the timbal buckles, caused by muscles attached to its surface. The singing of male cicadas in summer is caused by this mechanism.

VIBRATIONS CAUSED BY FLIGHT MUSCLES. Some insects produce sounds with their flight muscles when not flying. Honeybees use their flight muscles to make sounds important in social communication - during the bee dance in the hive, a forager gives some of the information regarding a nectar source with flight muscle sounds.

AIR EXPULSION. Some moths whistle or squeak by sucking air in through the mouth. Other moths and some beetles hiss by expelling air through their spiracles.