Hissing is a non-vocal acoustic signal widespread across the animal kingdom, serving as a primitive and effective form of communication. The sound is produced by the forced expulsion of air through a restricted opening in the respiratory tract. This turbulent airflow creates the characteristic, high-frequency, sibilant sound. Hissing is primarily a defensive sound, used by creatures from insects to large mammals. While the mechanism for creating this sharp sound varies significantly between animal classes, the resulting acoustic effect remains strikingly similar.
Hissing in Reptiles
Reptiles, particularly snakes, are the animals most commonly associated with the hiss, using it as a primary defense when threatened. The sound is generated through the glottis, the opening to the trachea. When a snake rapidly expels air, a small piece of cartilage within the glottis vibrates, creating the familiar sound.
Snakes like the cobra, rattlesnake, and African rock python employ this sound to deter predators or warn intruders. The intensity of the hiss is controlled by the force of the exhalation, which is often sustained by the snake’s elongated lung, allowing for a prolonged auditory threat display. Other reptiles also hiss, including large crocodilians like alligators, which use the sound to establish dominance, and monitor lizards when they feel cornered.
Hissing in Mammals
The mammalian use of hissing is most famously represented by the domestic cat, where the sound is a core part of its aggressive or defensive repertoire. Felids, including larger species like cougars, cheetahs, and leopards, produce the sound by pushing air forcefully over the back of the tongue and through a partially closed mouth. This mechanism allows the cat to display a threat without committing to a physical confrontation. The hiss is usually accompanied by a dramatic visual display, such as arched backs, flattened ears, and raised hackles, which maximizes the warning signal.
Other mammals also utilize this acoustic warning, though the context differs slightly. The Virginia opossum will hiss and growl when confronted, serving as an immediate warning before it resorts to feigning death. Badgers, such as the American badger, produce a sharp, cat-like hiss alongside growls and snarls as part of their aggressive defense posture. Hedgehogs, too, hiss when they are startled or irritated, often puffing up their quills simultaneously to create a more formidable impression. Even some rodents, like rats, will hiss when they are afraid or in pain.
Hissing in Birds and Invertebrates
The defensive hiss is found in birds and even some invertebrates. For birds, the sound is not produced by the syrinx, their vocal organ, but is an aerodynamic noise created by forced ventilation through the respiratory tract. Species like geese and swans aggressively hiss when protecting a nest or their young, making it a powerful territorial warning.
Cavity-nesting birds, such as the burrowing owl and certain tit species, produce a hiss-like call to deter predators investigating their dark nests. This acoustic signal is thought to mimic the sound of a dangerous snake, which may startle a potential mammalian predator. The most distinct mechanism for hissing occurs in the Madagascar Hissing Cockroach, which lacks lungs entirely. This insect forces air out of modified respiratory openings called spiracles, located on its abdomen, to create a loud, sustained hissing sound when disturbed.
The Purpose of the Hissing Sound
Across all these disparate animal groups, the primary function of the hissing sound is remarkably consistent: it serves as a powerful, immediate defensive warning. The sound is a form of acoustic aposematism, advertising that the animal is unprofitable or dangerous to attack. The sudden, sharp noise is designed to startle a potential predator, creating a momentary distraction that allows the animal to escape or launch a counter-attack.
In many cases, the hiss functions as a form of acoustic mimicry, known as Batesian mimicry, where a relatively harmless species imitates the sound of a truly dangerous one. The Blue Tit’s hiss, for instance, is acoustically similar to that of a snake, which may cause a predator to hesitate, associating the sound with a venomous threat.