Cicadas are well-known for the distinctive, loud sounds that fill warm summer days. These insect sounds are not random noise but produced through a complex biological process. This article will explore the fascinating mechanism behind how cicadas create their unique and intense acoustic displays.
The Tymbal Mechanism
The primary sound-producing organ in male cicadas is a specialized structure called the tymbal, located on each side of the insect’s abdomen. This structure consists of a rigid, ribbed membrane. Specialized muscles are attached directly to the tymbal membranes.
When these muscles contract, they cause the ribbed tymbal membrane to buckle inwards. As the muscles relax, the membrane snaps back to its original position. Each inward buckle and outward snap of the tymbal produces a distinct “click” sound. The speed and repetition of these actions are the source of the cicada’s sound.
Amplification and Resonance
The individual clicks produced by the tymbal are not loud enough to travel far. Cicadas possess an anatomical design that amplifies these sounds. Their abdomen is largely hollow, with air sacs functioning as a resonance chamber.
Sound waves from the vibrating tymbal membranes reverberate within this abdominal space, amplifying the sound. Flap-like structures called opercula cover the tymbal organs. These opercula can be moved by the cicada to modulate the sound and direct it outwards, enhancing its projection.
Types of Cicada Sounds
While the tymbal mechanism is fundamental, cicadas can produce a variety of sounds. They achieve this by varying the speed and rhythm of their tymbal contractions and adjustments to the opercula. Different cicada species produce unique sounds, patterns, and frequencies.
Cicadas create species-specific calling songs, often the loudest and most familiar sounds. They also produce alarm or distress calls when threatened or physically disturbed. These variations allow cicadas to communicate different messages using the same sound-producing structures.
The Purpose of Their Calls
Cicada sound production serves several biological purposes. The primary reason for their calls is to attract mates. Male cicadas produce species-specific calling songs, which are essential for signaling their presence to females of the same species.
These signals help males and females locate each other for reproduction. Some sounds also function as warnings. Cicadas produce a distress call when captured by a predator, startling the attacker or alerting others to danger.