Spiders, though often seen as land creatures, exhibit surprising interactions with water. While most are not truly aquatic, many possess remarkable adaptations allowing them to move on water surfaces or survive submerged for extended periods. These abilities are not universal across all species but highlight the diverse strategies arachnids employ to navigate their surroundings.
Movement on Water
Many spiders can move across the water’s surface without sinking, primarily due to surface tension. Water molecules at the surface create a resilient, skin-like layer. Spiders, being lightweight, distribute their weight across multiple legs, which are often covered in water-repellent (hydrophobic) hairs. This allows them to rest or glide on this “skin” without breaking through.
Some spiders, like fishing spiders (Dolomedes species), not only walk but actively propel themselves. They use their legs like oars, pushing against the surface tension for forward motion. This movement, akin to skating, creates small dimples in the water, effectively rowing them along. This allows them to hunt prey on the water or escape land-based predators.
Breathing Underwater
Most spiders are air-breathing and cannot directly extract oxygen from water. When submerged, some survive by trapping a thin layer of air around their bodies, forming a “physical gill” or “plastron.” Microscopic, hydrophobic hairs covering their abdomen, and sometimes their entire body, hold this trapped air in place.
This air film appears silvery underwater, creating a personal air supply. Oxygen from the surrounding water diffuses into this bubble, replenishing the spider’s supply as it consumes oxygen and releases carbon dioxide. This adaptation also prevents water from entering their respiratory openings and minimizes heat loss in cold water. Some common spiders can survive submerged for minutes, with species like Trechalea extensa observed hiding underwater for up to 30 minutes to evade predators.
True Aquatic Spiders
The diving bell spider (Argyroneta aquatica) is a notable example of a spider genuinely adapted to an aquatic lifestyle. This unique spider spends almost its entire life underwater in freshwater environments across Europe and Asia. It constructs a dome-shaped web between aquatic plants, filling it with air bubbles carried from the surface on its abdomen and hind legs.
This silk structure, known as a “diving bell,” functions as a stable underwater home and a larger, long-term physical gill. The spider can live, hunt, and reproduce within this air-filled chamber. The diving bell extracts oxygen from the water, allowing the spider to remain submerged for over 24 hours without returning to the surface.