The diving bell spider, Argyroneta aquatica, is the only known spider species that lives almost entirely underwater. This unique arachnid thrives in freshwater environments across Europe and Asia. Its ability to sustain itself submerged for extended periods highlights an extraordinary adaptation to an aquatic lifestyle.
Building the Underwater Air Bubble
The diving bell spider constructs an underwater home by weaving a silk web among submerged aquatic plants. This intricate silk structure serves as an anchor for its air reservoir. To fill this underwater dwelling, the spider makes repeated trips to the water’s surface.
During these trips, it traps a bubble of air using specialized, water-repellent hairs on its abdomen and hind legs. The spider then carries this trapped air down to its silk web, releasing it to gradually inflate the structure. This dome-shaped, temporary air chamber becomes its living space, providing a sheltered environment underwater.
The Secret of Continuous Air Supply
The air bubble functions as a “physical gill,” allowing continuous gas exchange with the surrounding water. Despite being a finite volume of air, this bubble actively draws oxygen from the water while expelling carbon dioxide. This gas exchange is driven by differences in partial pressure.
As the spider consumes oxygen, the oxygen partial pressure within the bubble decreases, creating a gradient that pulls dissolved oxygen from the higher partial pressure in the water into the bubble. Similarly, carbon dioxide produced by the spider’s respiration builds up within the bubble, increasing its partial pressure and causing it to diffuse out into the surrounding water. This process enables the spider to remain submerged for extended periods, often more than a day, without needing to frequently return to the surface.
While oxygen is replenished, nitrogen slowly diffuses out of the bubble, causing it to gradually shrink and eventually requiring a trip to the surface. The spider can also adjust the size of its bell to meet increased oxygen demands or adapt to lower oxygen levels in the water.
Beyond the Bubble: Other Aquatic Adaptations
Beyond its air bubble, the diving bell spider possesses several other aquatic adaptations. Its body is covered in specialized, water-repellent hairs, known as hydrofuge setae. These microscopic hairs trap a thin film of air around the spider’s body when submerged, giving it a distinctive silvery appearance. This trapped air allows the spider to carry oxygen outside its main bell and helps keep its body dry.
Male diving bell spiders are notably larger than females, a reversal of typical spider sexual dimorphism. This larger size and longer front legs in males enhance their efficiency in moving through water and overcoming buoyancy. They navigate their aquatic environment using silk draglines and by walking on plants.
From within or near its air bell, the diving bell spider is an active predator of small aquatic invertebrates, such as mosquito larvae, water mites, and even small fish. It ambushes prey, detecting their presence through vibrations in silk threads extending from its bell.
Reproduction also occurs entirely underwater, with mating and egg-laying taking place within the female’s larger diving bell. Eggs are laid in a silk cocoon, and spiderlings develop within this protected environment until ready to venture out.