Things You Might Not Know About Water Spiders

The water spider, also known as the diving bell spider, is the only spider that lives underwater. The reason for this adaptation may be the tough competition on land and the presence of terrestrial predators. Whatever the actual reason, this spider lives in water and builds an underwater structure known as a "diving bell," which helps it breathe. The scientific name of this spider is Argyroneta aquatica. One common subspecies of Argyroneta aquatica is the Japanese water spider. The only difference between these two sub-species is that the genital organs of the Japanese water spiders are larger than their European counterparts.

Physical Appearance and Behavior

Water spiders are usually small, with a light to dark brown cephalothorax and a dark velvety abdomen. Their average size is about 10 to 15 mm. Water spiders are unique in that the males are usually larger than the females, unlike most other spider species.

The male water spider can grow to 7.8 to 18.7 mm in length, while the female spider can be 7.8 to 13.1 mm long. A possible explanation for the larger size of males is their more active hunting style, which requires greater mobility and physical strength to overcome water resistance. Females, on the other hand, spend most of their time building and maintaining their large bells.

Though water spiders live in water, they do not have any gills. Instead, they have a unique way of breathing. Their legs and abdomen are covered with tiny hairs, which trap air bubbles. This trapped air gives the spider a silvery appearance underwater. The spider breathes from this bubble and carries it to an underwater web structure spun from silk.

The spider weaves a dome-shaped web among underwater plants and fills it with air bubbles collected from the water surface. This makes the web take a bell shape, which is why it is called a diving bell. This diving bell serves as an external gill for water spiders.

Oxygen from the surrounding water diffuses into the bell through the silk membrane, while carbon dioxide diffuses out. This is why the spiders do not need to come to the surface very often to top up the air supply. However, they do have to visit the surface occasionally, whenever the oxygen level drops too low or the carbon dioxide level rises too high.

Both the male and the female build air bells, though the male's bell is usually smaller than the female's. Males also replenish their oxygen less frequently than the females. The water spiders breathe through small openings under the abdomen, which are connected to their lung-like organ.

Habitat and Diet

Water spiders inhabit freshwater lakes and ponds, marshes, swamps, and slow-moving streams, mainly in the regions of central and northern Europe, through Siberia and Central Asia. The subspecies Argyroneta aquatica japonica, or Japanese water spider, can be found in Japan. These spiders are good swimmers, and they carry air on the fine hairs of the abdomen while swimming. Male water spiders are usually better swimmers and more aggressive hunters than the females.

The diet of these spiders consists of aquatic insects and crustaceans. Water mites, mayfly nymphs, and phantom midge larvae are some of the most common food sources of water (or diving-bell) spiders. They have strong fangs, and their bite can be quite painful. They usually use their venomous jaws to immobilize prey. When catching prey, they come out of the bell, then return to their underwater retreat to digest the food. Water spiders themselves sometimes fall prey to fish and frogs. Male spiders are more active during the day, while females and juvenile spiders are more active at night.

Frequently Asked Questions

What is the scientific name of the water spider?

Argyroneta aquatica

How does a water spider breathe underwater?

It traps air bubbles in the hairs on its body, then releases them into a dome-shaped silk web (a 'diving bell') that acts as an external gill.

Are male or female water spiders larger?

Males, unusually for spiders. Males can reach 18.7 mm; females reach 13.1 mm.

How many eggs does a water spider lay?

About 30 to 70 eggs, laid inside the female's diving bell.

Where do water spiders live?

Freshwater lakes, ponds, marshes, and slow streams in central and northern Europe through Siberia and Central Asia. The subspecies Argyroneta aquatica japonica lives in Japan.

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Reproduction

Unlike other spiders, the male water spider is usually larger than the female. Before mating, the male typically builds a diving bell near the female's bell. He also constructs a tunnel from his bell to hers in order to enter it. Mating takes place inside the female's bell. After mating, the female lays about 30 to 70 eggs in her bell. She usually creates a special chamber within the bell to hold the eggs.

After hatching, the young spiders do not immediately build their own bells. Instead, they fill up the empty shells of snails or similar structures with air, and use them as shelter for a while.

Molting and Hibernation

Like other spiders, water spiders molt (shed their skin). For this they often come out of the water onto nearby vegetation. Many times, though, they prefer to build a fresh bubble specifically for molting. Water spiders hibernate during cold winters. For this purpose they go deeper into the water, build sturdy diving bells, and seal the bells with silk. The spiders then stay inside their bells until the water warms up again.

The average lifespan of water spiders is about 2 years. The fangs of water spiders can pierce human skin, and the bite can cause inflammation and feverishness. The most remarkable thing about these spiders is the air bells they construct. These bells serve many purposes. Water spiders literally live, eat their prey, molt, mate, lay eggs, and raise their offspring safely within these bells, all while avoiding their terrestrial predators.

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