Diving Bell Spider

It brings its own air supply down and stores it. The spider's abdomen and hind legs are covered in a dense pile of water-repellent hairs that trap a thin layer of air whenever it surfaces, so it descends wearing a silvery bubble. It then wipes this air off into a purpose-built silk structure — the diving bell — anchored among plants, gradually inflating the bell into an air-filled dome large enough to sit inside. Crucially, the bell is not just a store — because oxygen diffuses from the surrounding water into the lower-pressure air of the bell, and carbon dioxide diffuses out, the bell acts as a physical gill. Research has shown a spider can stay in a well-made bell for over 24 hours, making only occasional trips up for a fresh bubble.

It is the only spider known to spend its entire life submerged. A number of other spiders can survive being underwater temporarily — some wolf spiders and fishing spiders dive to escape predators or catch prey and can breathe from a trapped air film for a while, and a few tropical species live in the intertidal zone. But those animals still live and reproduce in air. The diving bell spider hunts, feeds, moults, courts, mates, builds egg sacs, and rears its young all beneath the surface, coming out of the water essentially never. Everything about it, from the male being larger than the female to the design of its silk, is adapted to that life.

Like nearly all spiders it has venom, which it uses to subdue its aquatic prey, and it can bite a person if handled or trapped against skin. Reports describe the bite as painful, comparable to a bee or wasp sting, sometimes with localised swelling, inflammation, and a few hours of feeling feverish or unwell, but with no lasting harm and no confirmed serious cases. It is not an aggressive spider and encounters are rare because it lives out of sight underwater in ponds and ditches. Anyone pond-dipping or handling water plants where the spiders live should simply be a little careful.

It depends on a specific and shrinking habitat — clean, unpolluted, still or slowly flowing fresh water with dense submerged and emergent vegetation and good oxygen levels. Across Europe and Asia, many such ponds, ditches, fens, and lake margins have been drained, filled, dredged, shaded out, choked by nutrient pollution and algal blooms, or stocked with fish that eat the spiders. Because the physical-gill function of the diving bell only works well in water that is reasonably oxygen-rich and not too warm, eutrophication and warming directly undermine the spider's ability to breathe. It is still widespread but has disappeared from many local sites and is a protected or priority species in parts of its range.