Spiders, a diverse group of arachnids, are often associated with terrestrial environments, inhabiting a vast array of habitats from dense forests to arid deserts. Despite their common presence on land, questions frequently arise about their ability to interact with water. While the idea of a spider navigating an aquatic environment might seem unusual, some spiders demonstrate remarkable adaptations when encountering water. Their survival in or on water often involves unique physical characteristics and behaviors.
Spiders and Water: More Than Just Floating
Most spiders do not “swim” in the typical sense; instead, they employ specialized strategies to move across or survive on water surfaces. Their ability relies heavily on the physical properties of water, particularly surface tension. The cohesive forces between water molecules create a taut, film-like layer on the surface, which lightweight objects can exploit.
Spider exoskeletons are covered in microscopic, water-repellent hairs, making their bodies naturally hydrophobic. This quality prevents water from easily adhering, allowing them to remain dry even when in contact with water. This hydrophobic coating is present on various parts of their bodies, including their legs.
When a spider places its legs on the water’s surface, the water-repellent hairs create tiny indentations or dimples in the surface film. By distributing their weight across multiple legs, spiders avoid breaking this surface tension, effectively walking or “skating” across the water. This allows many species to move with ease on ponds, streams, or other bodies of water.
Some spiders also exhibit different gaits for water locomotion. They can use their middle pairs of legs like paddles for faster movement or even “row” by pushing their legs into the water to generate propulsion. Certain species can even raise their legs or abdomen to act as sails, utilizing wind to travel across the water’s surface. If accidentally submerged, the air trapped by their hydrophobic hairs helps them float back to the surface.
Breathing Underwater: The Air Bubble Strategy
While many spiders can navigate water surfaces, some species possess mechanisms to survive when fully submerged for extended periods. This ability is achieved not by breathing water directly, but by trapping an air bubble against their bodies. This trapped air acts as a “physical gill,” enabling the spider to extract oxygen from the surrounding water.
The spider accomplishes this using a dense layer of water-repellent hairs, particularly on its abdomen. These hairs create a surface that holds a thin film of air around the spider, giving it a silvery appearance underwater. This air bubble functions as a respiratory reservoir.
Oxygen from the water diffuses into the air bubble because the spider’s respiration continuously consumes oxygen within the bubble, creating a concentration gradient. Simultaneously, carbon dioxide produced by the spider diffuses out of the bubble and into the surrounding water. This continuous exchange allows the spider to obtain the necessary oxygen to survive underwater.
Some spiders can remain submerged for significant durations; for instance, some tropical spiders have been observed hiding underwater for up to 30 minutes using this air film. The air bubble also helps to minimize heat loss in cold water and prevents water from entering the spider’s respiratory organs.
Aquatic Specialists: Spiders That Truly Thrive in Water
A few spider species have evolved to become highly specialized in aquatic environments, demonstrating adaptations that allow them to spend nearly their entire lives underwater. The diving bell spider, Argyroneta aquatica, is the only known spider species to live almost exclusively beneath the water’s surface.
This spider, found in freshwater habitats across Europe and Northern Asia, constructs a unique underwater silk web. This structure, which resembles a bell or dome, serves as its permanent living quarters, a place for mating, and a nursery for its offspring. The spider regularly replenishes the air inside this “diving bell” by carrying bubbles from the surface, trapped by the hydrophobic hairs on its body.
The silk used for the diving bell is waterproof but allows for gas exchange, functioning as an external physical gill similar to the air bubble carried on the spider’s body. Oxygen diffuses from the water into the bell, supporting the spider’s respiration. Diving bell spiders can remain in their bells for over 24 hours, only surfacing to replenish the nitrogen that slowly diffuses out of the bubble. Unusually for spiders, the male Argyroneta aquatica is typically larger than the female, which may be linked to their aquatic lifestyle and mobility.
Another group of semi-aquatic specialists are fishing spiders (Dolomedes species). These large spiders hunt on or near the water’s surface. They detect ripples caused by prey, such as aquatic insects, tadpoles, or small fish, then rapidly move across the water to capture them. Fishing spiders can also submerge themselves, carrying a film of air that allows them to breathe underwater for a period, typically up to 30 minutes, to escape predators or pursue prey.