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).