Lots of spiders spend time on or in the water. Some can swim underwater for long periods to hunt or escape predators, and others have adaptations that let them simply survive underwater long enough to wait out flood conditions. But only one known species, Argyroneta aquatica, the water spider or diving bell spider, spends virtually its whole life underwater.
This species weaves a web resembling a diving bell that holds a pocket of air for the spider to breathe. The spider uses the bell as a base from which to hunt; the male goes into the female’s bell to mate, and the female builds an egg sac and lays her eggs all inside the bell. The silk of the web allows for gas diffusion between the air inside and the water outside, acting like a gill that takes in oxygen and lets out carbon dioxide, but it gradually shrinks due to net loss of nitrogen, so the spider has to pop up to the surface once in a while to refill it. The spider is covered in a layer of hairs that trap air bubbles next to the body, so it can leave its diving bell underwater and bring the air down to it.
I knew about trapdoor spiders and bolas spiders and all kinds of nutty spiders, but I had never heard of this scuba spider until today. It’s a good one.