Snakes do have a pair of external openings called nostrils, but their primary function is entirely different from those of mammals. These openings are not the main apparatus for the snake’s remarkable sense of smell. The reptile’s anatomical design separates the functions of breathing and chemoreception, which is the detection of chemical stimuli from the environment. This specialization allows snakes to navigate and hunt using a sophisticated sensory system.
Yes, Snakes Have Nostrils (But Not for Smelling)
The two external openings visible on a snake’s snout are called the nares, or nostrils, and their function is almost exclusively dedicated to respiration. Air enters through these openings, travels through the nasal passages, and reaches the trachea and lungs. Snakes typically breathe with their mouths closed, making the nostrils the main route for oxygen intake.
The structure of the respiratory system includes a specialized opening called the glottis, which is the entrance to the windpipe, located on the floor of the mouth. This feature becomes particularly important when the snake is consuming large prey. Since the act of swallowing can take a long time and completely obstruct the mouth and throat, the snake can extend the glottis forward. This extension allows the snake to move the breathing tube to the side of the meal, effectively functioning as a snorkel. The ability to reposition the glottis ensures that the snake can continue to draw air into its body even while its mouth is fully occupied.
The Unique Mechanism of Snake Scent Detection
A snake’s superior ability to “smell” the world relies on a two-part system involving its tongue and a specialized sensory structure, completely bypassing the nasal passages. The iconic, rapid flickering of the forked tongue is a deliberate action to collect minute, non-volatile chemical particles from the air, ground, or water. The tongue acts only as a transporter, gathering these scent molecules and preparing them for analysis.
Once the chemical samples are collected, the tongue is rapidly retracted back into the mouth and inserted into a pair of sensory pockets. These pockets are the openings to the Vomeronasal Organ (VNO), also known as Jacobson’s Organ, which is situated on the roof of the snake’s mouth. The chemicals are transferred directly onto the sensory cells within this organ, which is far more sensitive and specialized for chemoreception than the standard olfactory system.
The VNO is lined with highly specialized sensory neurons containing chemoreceptors that bind to and analyze the delivered molecules. This process allows the snake to interpret the chemical signals, which can identify a variety of factors, including the presence of prey, the proximity of a predator, or pheromones from a potential mate. The information is then transmitted to the accessory olfactory bulb in the brain for processing.
The evolutionary advantage of the snake’s bifurcated, or forked, tongue is its role in “stereo-olfaction,” which is the ability to sense direction. Since each tip of the tongue delivers chemicals to a separate side of the paired VNO, the snake’s brain can compare the relative concentration of the scent on each side. If the chemical signal is stronger on the right tip, the snake knows the source of the scent is to the right, enabling it to follow a trail with remarkable accuracy.