There is only one species of spider in the world that spends its entire life underwater. It is called the diving bell spider or the water spider. A spider that lives underwater is amazing enough but to make matters mind-blowing, the spider uses a "diving bell" or bubble of water that actually acts like a lung!
Found in ponds in Europe and Asia, these small spiders have adapted to hunt for insects and crustaceans under the surface, living safe from land-dwelling predators though they aren't safe from frogs and fish. They have made this transition from living on land to underwater by devising a SCUBA tank of sorts. Using silk to form a "bell", the air-breathing spiders trap air in hairs on their abdomen and legs at the surface of the water and fill the bell with the trapped air. They can then live inside the bell, and in fact females live almost their entire lives inside the bell only coming out to snatch prey or to refill their air supply.
But refilling happens rarely and here's the mind-blowing part: unlike our own SCUBA tanks that have to be refilled when we use up all the air, these diving bells can replenish the air supply on their own.
"As the spider consumes oxygen from the air in the bell, it lowers the oxygen concentration inside. The oxygen can decrease below the level of dissolved oxygen in the water, and when this happens, oxygen can be driven into the bubble from the water," said Prof Roger Seymour