The Star-Nosed Mole, Condylura cristata, is a small mammal found in the wet environments of eastern North America. It is defined by a single, highly specialized sensory organ surrounding its nostrils. This fleshy, pink structure is one of the most distinctive adaptations in the animal kingdom. Its function is primarily for touch, allowing the mole to navigate and hunt in the dark with astonishing efficiency in its subterranean and aquatic world.
The Star: Anatomy and Eimer’s Organs
The structure that gives the star-nosed mole its name is a single, radially symmetrical arrangement of 22 fleshy appendages. These appendages, or rays, extend outward from the snout in 11 pairs around the nostrils. They are in constant, rapid motion as the mole explores its environment. The entire star is a concentrated sensory device, measuring only about one centimeter in diameter.
The surface of these rays is covered in a dense array of specialized touch receptors known as Eimer’s organs. Each star contains more than 25,000 of these microscopic, domed papillae, which are unique to moles. This dense concentration of sensors is innervated by over 100,000 nerve fibers. This gives the star one of the highest densities of nerve endings of any known mammal, making it ultrasensitive to even the slightest physical contact.
The 22 rays are physically differentiated to perform different roles in the mole’s sensory mapping. The longer, outer rays are used for general physical investigation, sweeping the immediate surroundings. When these outer rays detect a point of interest, the star shifts quickly. This allows the two shortest, central rays—the eleventh pair—to be pressed onto the object. This central pair functions as a high-resolution tactile fovea.
Sensory Superiority: How the Star Hunts
The star is the primary tool the mole uses to locate and identify prey, turning the absence of light into an advantage by relying on an acute sense of touch. The mole is often cited as the fastest foraging mammal on Earth, a title earned through its lightning-fast sensory processing and decision-making. When searching for food, the mole sweeps its star across the ground, touching up to 13 separate areas every second.
This touch-and-go method allows the mole to quickly create a high-resolution map of its immediate surroundings. Sensory information is relayed to its brain at a speed approaching the physiological limits of neuronal transmission. Once the tactile fovea makes contact with a potential prey item, the mole can identify it as edible and consume it in as little as 120 milliseconds, demonstrating the incredible efficiency of the mole’s nervous system.
The mole’s brain processes the tactile information and determines the edibility of the object in a mere eight milliseconds. This rapid decision-making capability allows the mole to maintain its astonishing foraging speed. The star’s function as a tactile fovea means that the two central rays are disproportionately represented in the mole’s somatosensory cortex, much like the visual cortex in primates.
While the star’s primary function is mechanoreception, this unique sensory adaptation has also been studied for its potential to detect weak electrical fields. Some researchers suggest the mole may possess a form of electrosensitivity, particularly when hunting aquatic prey in muddy water where sight and touch are hindered. Though evidence is limited compared to its tactile abilities, this possibility suggests the star is a multi-functional sensory device adapted to challenging environments.
Subterranean Life and Habitat
The star-nosed mole is a semi-aquatic species, preferring the moist, low-elevation areas of eastern North America, from southeastern Canada down to the northern parts of the southeastern United States. It thrives in wetlands, marshes, swamps, and along the banks of lakes and streams, which provide the soft, saturated soil it needs for burrowing. Its body is well-suited to this environment, covered in thick, water-repellent fur and possessing large, paddle-like forelimbs for digging and swimming.
The mole constructs a complex system of tunnels that are often shallower than those of other mole species, allowing it to forage close to the surface. A unique feature of its burrow system is that the tunnels frequently open directly into water, reflecting the mole’s reliance on aquatic prey. The mole is an active forager year-round and does not hibernate, often having to swim beneath the ice in winter to find food.
The star-nosed mole’s diet is predominantly carnivorous, consisting of small invertebrates found both on land and in water. Its main food sources include earthworms, insect larvae, mollusks, and small crustaceans. The mole is an excellent swimmer, using its star organ to probe bottom sediments for aquatic prey. It is also capable of a unique form of underwater “smelling,” exhaling air bubbles onto objects and quickly re-inhaling them to carry the scent back to its nostrils.