Diving bell spider

 It is the only spider known to spend its whole life under water. As with other spiders, it breathes air, which it traps in a bubble held by hairs on its abdomen and legs. This gives it a silvery appearance, despite it being velvet-grey. The spider inhabits ponds in Europe and northern Asia, and lives for approximately two years.
Females build underwater "diving bellwebs which they fill with air and use for digesting prey, molting, mating and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the silk threads that anchor it. However, they have to surface occasionally to renew their personal air supplies and those of their webs. Males also build bells, but these are smaller and the males replenish their bells' oxygen supply less often. The males also have a more active hunting style. Prior to mating, the male constructs a diving bell adjacent to the female's, then spins a tunnel from his bell, breaking into hers to gain entrance. Mating then takes place in the female's bell. The female spider lays between 30 and 70 eggs in her bell.
Males are around 30% larger than females, which is unusual for spiders. This is possibly because their more active hunting style requires greater strength to overcome water resistance and counteract the buoyancy of their mobile air supplies. The larger body size is also associated with longer front legs, which has been shown to affect diving ability, giving the males superiority in diving over the more sessile females. The size of females may be limited as they put more energy into building and maintaining their larger bells. The spiders prey on aquatic insects and crustaceans. Their bite is quite painful as the fangs can pierce the skin, causing localised inflammation and feverishness. The spiders themselves fall prey to frogs and fish.

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