Scorpions are creatures of the night, and their nocturnal habits raise questions about how they navigate and hunt in darkness. While scorpions possess multiple eyes, their survival is not solely dependent on vision. Their ability to thrive in low-light conditions results from a complex sensory system where sight is just one component.
The Anatomy of Scorpion Eyes
Scorpions possess two types of simple eyes, known as ocelli. A pair of median ocelli is centrally located on top of their carapace, or head shield, and are larger and more prominent than their other eyes. In addition to the median pair, scorpions have groups of lateral ocelli on each side of the carapace.
The number of these lateral eyes can vary considerably among species. While most scorpions have one pair of median eyes, the number of lateral eye pairs can range from zero to five. This means a scorpion can have anywhere from two to twelve eyes, and this arrangement is used to classify different species.
The Function of Scorpion Vision
Despite having numerous eyes, a scorpion’s vision is not sharp and cannot form detailed images. Their central eyes are among the most light-sensitive in the animal kingdom. This sensitivity does not provide clarity but is instead tuned to detect subtle changes in light intensity, which is important for their survival.
This light-sensing ability allows them to perceive the shadows of predators or prey moving overhead. It is also used for navigation, as scorpions can use faint light from the moon and stars to orient themselves. This perception of light regulates their nocturnal activity, telling them when to hunt and when to remain hidden.
Sensing the World Without Sight
Since their eyesight is poor for details, scorpions rely heavily on other senses to hunt effectively. They perceive their world primarily through touch and vibration, constructing a sensory map that compensates for their lack of sharp vision. This non-visual perception makes them successful nocturnal predators.
Fine sensory hairs on their pincers and legs, called trichobothria, are sensitive enough to detect minute air currents from a flying insect. They also pick up vibrations transmitted through the ground, allowing the scorpion to determine the direction and distance of its prey. By measuring the time it takes for a vibration to reach each leg, it can calculate the exact location of its next meal.
Unique, comb-like structures on their underside called pectines also contribute to their sensory world. These organs are covered in chemical sensors that “taste” or “smell” the ground. Males use their pectines to track pheromones left by females, while both sexes may use them to navigate and locate prey. Slit sensilla on their legs detect deformations in the exoskeleton from ground vibrations, adding another layer of sensitivity.