Locusts are a phase of certain short-horned grasshoppers that shift from a solitary existence to a highly social, migratory swarming state. This change is driven by environmental conditions, particularly when population density increases and food resources become scarce. The intense aggregation necessitates acoustic communication, making sound production a significant factor in their life cycle. Their sounds function for communication, such as mate attraction, and mark their mass movement during swarming phases.
The Specific Sound Profile
The noise produced by a locust varies depending on the species, activity, and whether the insect is solitary or part of a swarm. Individually, many locust species generate a soft, muffled buzzing or a series of clicks. This sound is used for close-range communication, such as reproductive purposes or warning signals.
When a massive group takes flight, the sound transforms into a louder, more continuous acoustic experience. A flying swarm produces a collective sound described as a loud, continuous buzzing or a persistent rattling and crackling noise. This amplified sound results from millions of insects moving simultaneously. For some species, the sound includes a distinct snapping or cracking element, known as crepitation, which occurs as the insects stretch their wing membranes taut during flight.
How Locusts Produce Sound
The primary method locusts use to generate sound is stridulation, which involves rubbing two specialized body parts together. This process is analogous to drawing a bow across the strings of a violin, converting mechanical friction into an acoustic signal.
In many species, sound is created by rubbing the inner surface of the hind legs, equipped with small spikes, against the edges of their forewings. This action causes rapid vibration, producing the characteristic buzzing or chirping noise. Stridulation is a deliberate action used for social signaling, such as attracting a mate or signaling territorial boundaries.
A secondary form of sound production is crepitation, the loud, snapping sound made by the wings during flight. This sound is not produced by friction but by the rapid expansion and tensioning of the wing membranes. Crepitation is often heard in band-winged locusts and is a byproduct of their locomotion, adding a distinct crackling layer to the overall sound of a flying swarm. Both stridulation and crepitation fall under the order Orthoptera’s general sound production methods.
Differentiating Locust Sounds from Other Insects
The sound of a locust is often confused with that of other insects, particularly cicadas and crickets, but their sound production mechanisms are fundamentally different. Locusts rely on friction-based stridulation and movement-based crepitation, resulting in sounds typically ranging from clicking to a moderate buzzing, usually around 50 to 70 decibels. This volume is generally quieter than the sustained noise of a cicada.
Cicadas generate sound using specialized organs called tymbals. These paired, drum-like membranes are located on the sides of the male cicada’s abdomen and are vibrated rapidly by muscular action. This mechanism produces a sustained, high-volume droning or high-pitched sound that can reach 90 to 100 decibels, making it louder and more continuous than the locust’s noise.
Crickets also use stridulation, rubbing their forewings together, but the resulting sound quality is a distinct, rhythmic chirp rather than the locust’s erratic buzz or snap. The difference in sound production mechanisms—friction for locusts and crickets versus membrane vibration for cicadas—accounts for the variation in volume, pitch, and texture, providing a clear distinction between these insects.