A sustained, fluctuating, and distant loud sound can often be mistaken for a faraway siren or mechanical alarm. This common auditory experience frequently prompts curiosity, leading many to wonder about its source and whether it originates from an emergency vehicle or something else entirely.
The Cicada: Nature’s Siren
The cicada is the insect responsible for this siren-like sound in nature, renowned for its loud calls. Cicadas produce a characteristic buzzing, whirring, or chirping sound that can be sustained for long periods, often varying in pitch and intensity, which contributes to its resemblance to an oscillating siren. Different cicada species exhibit variations, from rhythmic clicks to high-pitched whines.
Cicadas do not use vocal cords. Instead, male cicadas possess specialized structures called tymbals on their abdomen. These thin, ribbed membranes are connected to powerful muscles. When the cicada rapidly contracts and relaxes these muscles, the tymbals buckle inward and then pop back, creating rapid clicks. This fast vibration produces the continuous buzzing sound. The male cicada’s hollow abdomen and tracheal air sacs then amplify this sound, allowing it to travel long distances.
The loud calls serve a biological purpose, primarily to attract mates, as only male cicadas produce these sounds. The volume helps them overcome environmental noise and reach potential mates. Cicadas may also produce sounds as a distress signal when threatened. Their emergence periods vary, with annual cicadas appearing every summer and periodical cicadas emerging in synchronized broods every 13 or 17 years, influencing when their distinctive calls are heard.
Why the Confusion?
The resemblance between cicada calls and man-made sirens stems from auditory perception and environmental factors. The human ear perceives the cicada’s loud, high-pitched, and fluctuating sound, especially when heard from a distance, in a way that mimics a siren’s oscillating tone. As sound travels, higher frequencies can become more attenuated, making it harder to pinpoint its exact origin or nature.
Environmental factors also contribute to this auditory illusion. The sheer density of cicadas during mass emergences can amplify their collective sound to significant decibel levels. The time of day also plays a role, as cicadas are often loudest during warmer parts of the day. Sound reflection and absorption in urban or suburban environments, such as off buildings or through dense foliage, can distort the sound, making it seem like a mechanical alarm with an unclear source. Since cicadas often reside high in trees and are out of sight, the disembodied nature of their sound increases the mystery and contributes to misidentification.
Distinguishing Animal Sounds from Man-Made Alarms
Discerning between cicada calls and man-made sirens involves specific sound qualities and contextual cues. Real sirens typically exhibit a mechanical, rhythmic pattern with distinct starts, stops, and consistent modulations. In contrast, cicada sounds, while loud, tend to be more organic, continuous, or feature natural, less precise fluctuations in their buzzing or whirring.
Cicada sounds are seasonal, primarily heard from late spring through early fall in areas with trees and vegetation. Sirens, conversely, can occur anywhere at any time. While cicada calls can be sustained for long durations, emergency vehicle sirens often have more precise repetition and duration patterns. The absence of visual cues, such as flashing lights or emergency vehicles, can strongly indicate an animal source. Awareness of local cicada emergence cycles also helps in accurately identifying the sound.