Diving bell spider
The diving bell spider or water spider, Argyroneta aquatica, is the only species of spider
Spiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...

 known to live entirely under water.

Argyroneta aquatica is found in northern and central Europe and northern Asia up to latitude 62°N
62nd parallel north
The 62nd parallel north is a circle of latitude that is 62 degrees north of the Earth's equatorial plane. It crosses the Atlantic Ocean, Europe, Asia and North America....

. 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" web
Spider web
A spider web, spiderweb, spider's web or cobweb is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets....

s 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
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

 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.

The appearance of the diving bell gave rise to the genus name Argyroneta, from the Greek "argyreios" (αργυροειδής), meaning "silvery", and "netos" (νήθωσ) meaning in context: "spun". However, frequent replenishment at the surface is unnecessary in well-oxygenated water, because the structure of the bell permits gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...

 with the surrounding water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

: oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 is replenished and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 expelled by diffusion. The process is driven by differences in partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

 and relative solubility in water, of nitrogen, oxygen, and carbon dioxide. In summary, as oxygen in the bubble is used up, more can diffuse in, whereas as carbon dioxide accumulates, it dissolves in the water and is lost. This system has been referred to as "the water spider's aqua-lung
Aqua-Lung was the original name of the first open-circuit free-swimming underwater breathing set in reaching worldwide popularity and commercial success...

 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 continuous exchange of oxygen and carbon dioxide with the gases dissolved in the water.

The prey of these spiders includes various aquatic insects and crustaceans. Their fangs are robust enough to pierce human skin and the bite is said to be quite painful, causing localised inflammation and feverish symptoms. The spiders themselves fall 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 pond
A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens, water features and koi ponds; all designed for aesthetic ornamentation as landscape or architectural...

s near the palaearctic region, which includes Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, northern Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

, and Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

 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.

External links

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