THE DIVING BELL SPIDER (Water spider).

 Argyroneta aquatica is found in northern and central Europe and northern Asia up to latitude 62°N. It is the only spider known to spend its whole life under water. However it breathes air, which it traps in a bubble held by hairs on its abdomen and legs.
 Females build underwater "diving bell" webs 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. Although they are better swimmers than females, they prefer to cling to silk threads or underwater vegetation while moving.
 Very unusual for spiders, males of this species are about 30% percent larger than females, possibly because their more active hunting style requires greater strength to overcome the resistance of the water and to counteract the buoyancy of their mobile air supplies. The sizes of females may be limited by the amount of energy they put into building and maintaining their larger bells.
 The spider web can serve as underwater gills for the spider exchanging carbon dioxide with oxygen in the surrounding water.
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