Diving bell spider

The diving bell spider or water spider, Argyroneta aquatica, is a spider which lives entirely under water, even though it could survive on land.

Description

Since the spider must breathe air, it traps a thin layer of air around its body using the hairs on its abdomen and legs. It also maintains an air reserve in a "diving bell" constructed from silk, which it anchors to an underwater plant. The appearance of the diving bell gave rise to the genus name Argyroneta, Latin for "silvery net". The spider can replenish the air in its bell by transporting air from the surface. However, frequent replenishment is unnecessary because the structure of the bell permits gas exchange with the surrounding water: oxygen is replenished and carbon dioxide expelled due to differences in osmotic pressure. This system has been referred to as "the water spider's aqualung of air bubbles," but it is actually more advanced than the real Aqualung®, which needs to be refilled frequently with compressed air, not having the option of osmotic exchange. This air supply allows the spider to remain in the bell for long periods, where it waits for its prey. The spiders are themselves prey to frogs and fish. Prior to mating, the male constructs a diving bell adjacent to the female's before spinning a tunnel from his bell to hers and then breaking through her wall to gain entrance. Mating takes place in the female's bell, after which the female spider lays from 30 to 70 eggs there. The spider is found in ponds in the palaearctic region, which includes Europe, northern Asia, and Africa north of the Sahara desert. It lives for approximately two years. It is velvet-grey, although the trapped air around its body gives it a silvery appearance. Unusually for spiders, the males (9 - 12 mm) of this species are often larger than the females (8 - 15 mm). One subspecies is native to Japan:

• Argyroneta aquatica japonica Ono, 2002

External links

• http://mmem.spschools.org/grade5science/wetland/waterspider.html