[6][8] A. aquatica is the only known species of spider that spends almost all its life underwater, including resting, catching and eating prey, mating, egg laying, and overwintering.

[16] Numerous species, including some Ancylometes, Dolomedes, Megadolomedes, Pardosa, Pirata, Thalassius and others, live above water at the surface, but may actively submerge for a prolonged period, are strong swimmers and will catch underwater prey.

[9][18] A. aquatica is found in clean freshwater habitats with aquatic vegetation, such as lakes, ponds, canals, marshes and slow-moving streams.

[7][21] South Korea has a protected area, Yeoncheon Eundaeri water spider habitat,[22][23] for this endangered species in that country.

[7] This size differential favoring males is unusual for spiders, where sexual dimorphism is usually in favour of larger females.

Theories suggest that the male's more active hunting style requires greater strength to overcome water resistance and counteract the buoyancy of their mobile air supplies.

[11] Diving bells are irregularly constructed sheets of silk and an unknown protein-based hydrogel[29] which is spun between submerged water plants then inflated with air brought down from the surface by the builder.

However, there is net diffusion of nitrogen out of the bell, resulting in a gradually shrinking air bubble which must be regularly replenished by the spider.

These spiders voluntarily tolerate internal conditions of low oxygen, enlarging their bells with air when the P(O2) drops below 1 kPa; this replenishment process may not need to occur for several days, in some cases.

Their bite is often described as being very painful to humans and as causing localised inflammation, vomiting, and slight feverishness that disappears after 5–10 days.