Tarantulas are among the largest spiders globally, recognized for their impressive size and dense coat of hair. As terrestrial creatures, their natural habitat is typically dry burrows or arboreal crevices. These large arachnids can indeed move across the surface of water, which is a subject of common fascination.
The Direct Answer and Necessary Context
A tarantula can traverse a water surface when necessary, though this movement is not “walking” like a water strider. Instead, it is a combination of buoyancy and propulsion, often described as floating or rowing. The spider rests on the water’s surface film, using its long legs to push itself forward. This movement is primarily an emergency maneuver, typically employed as a quick escape from a threat or a temporary solution to a flooded environment.
Once on the water, the tarantula uses its first three pairs of legs to row, moving them out of phase like paddles to propel its body. The action is forceful enough to create forward momentum. The fourth pair of legs is often trailed behind, helping to stabilize the body as it glides across the surface.
The Physics and Biology of Water Movement
This feat relies on a combination of physics and the tarantula’s specialized anatomy. The primary physical principle is surface tension, which causes the top layer of water to act like an elastic film strong enough to support the spider’s weight.
The tarantula’s body and legs are covered in a dense layer of fine, specialized hairs called setae. These hairs are hydrophobic, meaning they actively repel water. This water-repellent nature prevents water from adhering to the spider, effectively keeping it dry.
The dense hair layer traps a thin cushion of air around the spider’s legs and body. This air cushion increases buoyancy and distributes the spider’s weight across a larger area of the surface film. By preventing the surface tension from breaking, the tarantula remains suspended on top of the water.
Behavioral Context and Limitations
Tarantulas generally only enter the water when forced, such as when their burrows flood or when fleeing a predator. They possess sensory organs on their legs, known as hygroreceptors, which detect humidity and alert the spider when it is in contact with water. This movement is a short-term survival strategy, not a regular form of locomotion.
While they can move across the surface, this ability has limitations, especially regarding turbulent water or prolonged exposure. Tarantulas breathe using book lungs, which are internal respiratory organs composed of stacked, plate-like structures. These organs extract oxygen from the air, not from water.
If the spider is forced completely underwater for an extended period, or if the water is too choppy, it risks submersion. This can lead to drowning due to the inability of the book lungs to function.