Snakes are highly specialized reptiles whose sensory world operates differently from that of mammals. Chemoreception, the ability to perceive chemicals in the environment, is their most developed sense, compensating for limited vision and hearing. The characteristic act of a snake constantly flicking its tongue is central to this process. This article explains the unique anatomy and process snakes use to perceive their surroundings.
The Primary Use of Snake Nostrils
Snakes possess external openings on their snout called nostrils, or nares. These structures are not used primarily for detecting scents; their main function is respiration. Like other vertebrates, the nostrils lead to a nasal cavity, allowing air to pass into the lungs.
The nasal passages contain rudimentary olfactory sensors, and snakes can technically perceive airborne odors this way. However, this method is far less sensitive and less important for navigation and hunting than their specialized internal organ. The nostrils serve mainly as a pathway for oxygen, allowing the snake to breathe even while its mouth is full of prey.
The Unique Mechanism of Snake Smell
The sensory process snakes use to interpret their environment centers on the interplay between the tongue and an internal structure. The rapid flicking of the forked tongue is a method of collecting chemical samples from the air and ground. The tongue’s moist surface captures tiny, non-volatile odor molecules.
The specialized tongue is deeply forked, splitting into two separate tines at the tip. This dual structure enables stereo-olfaction, functioning like two separate sampling devices. By picking up slightly different concentrations of scent particles on each fork, the snake’s brain can rapidly calculate the direction from which the odor is coming.
Once the tongue is retracted, the collected scent molecules must be transferred for analysis. The tips of the two forks are precisely inserted into a pair of small openings on the roof of the mouth. These ducts lead directly to the sensory organ responsible for processing chemical information.
This processing center is known as the vomeronasal organ, or Jacobson’s organ, a pair of fluid-filled sacs. The odor particles delivered by the tongue dissolve in the fluid, stimulating specialized chemoreceptors that send signals to the accessory olfactory bulb of the brain. The vomeronasal system is adept at detecting complex chemicals, such as pheromones, that would not stimulate the simpler receptors in the nasal cavity. The constant flicking, which can occur once per second or faster when tracking, ensures a continuous stream of up-to-date chemical information is fed into this internal sensor.
How Scent Guides Snake Behavior
The chemical sensing system guides nearly all of a snake’s fundamental behaviors. Tracking prey is one of the most important uses of this heightened chemoreception. Snakes can follow faint chemical trails left by small mammals, birds, or other reptiles across various surfaces.
Once a venomous snake strikes and releases its prey, following a precise scent trail is crucial for relocating the animal after it has moved away to die. This allows the snake to conserve energy and avoid a dangerous struggle.
For reproductive purposes, the sense of smell is equally vital for locating a mate. Female snakes release species-specific chemical signals called pheromones, which are easily detected by the male’s vomeronasal organ. Males follow these pheromone trails over long distances, sometimes even following the chemical trail left by a female’s shed skin.
Chemoreception is also used for general navigation and finding shelter. Young garter snakes, for instance, utilize scent trails left by their mothers to locate communal den sites, known as hibernacula, before winter. Continuous sampling allows snakes to identify and avoid the chemical signatures of predators or to find optimal basking and resting spots.