Water spider  (Argyroneta aquatica)

The water spider is not currently threatened (2).

The water spider (Argyroneta aquatica) is the only spider in the world that spends its entire life under water (3). The body of the water spider is densely covered in short hairs that trap air when the spider is submerged (2), and enables the it to transport air bubbles down to a ‘diving bell’ it constructs from silk (3). Although the water spider is velvet-grey out of the water, when it is in the water the air trapped around its body gives it a silvery appearance, which has been likened to quick-silver (mercury) (1). This is one of the very few spiders in which the males are larger than the females (4). Although the water spider has been placed in a separate family, the Argyronetidae, recent scientific studies examining fossil spiders suggest that it should be placed in the family Cybaeidae (5).

The water spider occurs in Britain (2), throughout northern and central Europe, in Siberia and northern Asia (6).

You can view distribution information for this species at the National Biodiversity Network Gateway.

An inhabitant of ponds, slow-moving streams, ditches, and shallow lakes, the water spider favours areas where there is plenty of aquatic vegetation (2).

The water spider is remarkably adapted to its underwater life. It spins an underwater retreat amongst the weeds, which it fills with air by travelling up to the surface and returning to the retreat, carrying air bubbles trapped in the fine hairs on the body (2). As it fills with air, the retreat becomes bell-shaped and takes on a silvery sheen. The scientific name of this species, Argyoneta, derives from the Latin for ‘silvery net’, and refers to this unique air-bell that the species creates. Amazingly, the spider only has to replenish the air-supply in the bell occasionally, as oxygen diffuses in from the surrounding water and carbon dioxide diffuses out (7). When in its ‘diving bell’ retreat, the water spider breathes normally, as if on land, while outside of its retreat, it is able to breathe through its skin using the layer of air trapped on its body (3) (8).

A largely solitary species, the water spider is mainly active at night. Males tend to be more active then females and actively hunt their prey. In contrast, females spend most of the time inside the air-bell and catch prey that strays too close to the bell (9). Prey species include small aquatic invertebrates such as water boatmen and tadpoles (1).

Males will mate with females after building an air-bell next to that of a female. The male then bites through and mates with the female. The female spins a cocoon around the eggs at the top of her air-bell. The young spiders hatch after a few weeks and disperse (1). Before hibernating, the water spider seals up its air-bell or occupies an empty shell, which it lines with silk (1).

The water spider is not threatened.

Conservation action is not required for the common water spider.

There may be further information about this species available via the National Biodiversity Network Gateway.

Discover more about invertebrates and their conservation:

• Buglife:
  http://www.buglife.org.uk/

 More information on British spiders:

• The British Arachnological Society:
  http://www.britishspiders.org.uk/