The water spider, Argyroneta aquatica, is the only spider known to spend almost its whole life underwater. It lives in still or slow-moving fresh water across Europe and temperate Asia, where it builds a silk “diving bell” among water plants and fills it with air carried down from the surface. It is also called the diving bell spider.
The name “water spider” is also used loosely for fishing spiders that hunt along the edges of ponds and streams, especially in Australia. Those are different spiders, covered near the end of this page.
Water spider at a glance
| Scientific name | Argyroneta aquatica (Clerck, 1757) |
|---|---|
| Other common name | Diving bell spider |
| Family | Argyronetidae (earlier placed in Cybaeidae, then Dictynidae) |
| Body length | Males about 10–15 mm; females about 8–9 mm (body only, not including legs) |
| Native range | Europe, Turkey, the Caucasus, Russia east to the Far East, Iran, Central Asia, Mongolia, China, Korea and Japan |
| Habitat | Clean, weedy ponds, lakes, ditches, canals and very slow streams |
| Diet | Small aquatic animals, mainly invertebrates |
| Contact with people | Rarely seen and rarely handled; it may bite if roughly handled |
The genus Argyroneta contains just this one species. For a long time it was classified with other families, most recently Dictynidae. After a 2025 revision of that group, the World Spider Catalog now lists it in the family Argyronetidae. A Japanese subspecies, Argyroneta aquatica japonica, is also listed in the catalog.
How to recognize a water spider
The most useful clue is not its color but where it is and what it is doing. A spider moving around under the surface of a pond, among submerged plants, with a shining silver coat of air, is very likely a water spider within its range. No other spider in Europe or Asia lives this way.
- Silvery look underwater. Air trapped by fine hairs on the abdomen, and on the underside of the body, gives the spider a mirror-like sheen in the water.
- Plain brown to grey out of water. Without its air layer, the spider looks mid to dark brown. The hairs on the abdomen can make it appear dull grey and velvety.
- Swimming position. It often swims with its underside facing upward.
- Hairy back legs. The fourth pair of legs carries especially long hairs, some arranged in tufts, which help it hold and move air.
- Silk bells among plants. Small air-filled silk domes attached to water weeds are a strong sign that water spiders live in a pond.
Geography matters too. The World Spider Catalog’s range for this species does not include the Americas or Australia, so a “water spider” seen on a dock in North America or by a creek in Australia is almost certainly a different kind of spider. For a general method of narrowing down an unknown spider, see our spider identification guide.
How the diving bell works
The water spider still breathes air, just like land spiders. What makes it unusual is how it keeps a supply of air underwater.
First, it spins a sheet of silk between the stems of submerged plants. It then swims to the surface, traps a bubble of air against its hairy abdomen and legs, and carries it back down. Released under the silk, the air collects into a dome. Repeated trips enlarge the bubble into a bell big enough for the spider to sit inside.
Older books often said the spider had to fetch new air every 20 to 40 minutes. A 2011 study by Roger Seymour and Stefan Hetz measured oxygen inside real bells and found that the bell works like a physical gill. As the spider uses oxygen, more oxygen moves into the bubble from the surrounding water. Even in warm, stagnant water, this was enough to meet the spider’s needs.
The bell still shrinks slowly, because nitrogen gradually leaks out of it into the water. Based on that rate, the researchers calculated that in their test conditions a spider might only need to top up its bell about once a day. Staying hidden for long periods may help it avoid predators and stay unnoticed by prey.
The bell is used for almost everything: resting, eating, mating, laying eggs and surviving winter. For more on how spiders use silk in everyday life, browse our spider behavior articles.
Where water spiders live
Water spiders need clean fresh water with plenty of underwater plants and little or no current. Typical places include ponds, small lakes, drainage ditches and dykes, canals and very slow streams.
Plants matter because they hold the silk bells in place. A field study in northern Italy found that water spiders were more likely to be present where there was aquatic vegetation, plenty of prey and few predators.
In Britain, the British Arachnological Society describes the species as widespread but scattered in the south and much more local further north. It can be numerous where the habitat suits it, but pollution of fresh water is thought to be causing declines in some areas. You can read more about how different spiders use their surroundings on our spider habitat page.
What water spiders eat and how they hunt
The water spider is an ambush hunter. It waits in or near its bell, often with silk threads running out from it, and darts out when suitable prey passes. It then takes the catch back to the bell, or sometimes to the surface, to eat it in the air.
Its prey is mostly small aquatic invertebrates, such as aquatic insects and their larvae and small crustaceans. The Wildlife Trusts note that it rests in its bell during the day and hunts at night. For a wider look at how spiders find and handle food, visit our spider diet section.
Mating, eggs and winter
Mating takes place at the female’s bell. In late spring and early summer, the female builds a separate silk egg chamber, lays her eggs inside and guards them. Young spiders can later be found among the water plants.
In late autumn, water spiders move into deeper water where they are less likely to be trapped by ice. There they build a stronger, air-filled retreat, close it up and stay inside until early spring.
Why male water spiders are bigger
In most spiders, females are larger than males. The water spider is a well-known exception: adult males are usually bigger.
Research on populations near Vienna, published in 2003 by Dolores Schütz and Michael Taborsky, suggests two reasons:
- Males benefit from moving well underwater. Males roam to find females, and in diving tests males were the better divers, mainly thanks to their longer front legs.
- Females may face limits on size. Females build larger bells, and in the experiments they had to fetch air from the surface more often than males. The authors suggest that the cost of maintaining a bell may limit how large females become.
Do water spiders bite?
Water spiders are venomous, like almost all spiders, but people very rarely come into contact with them. The British Arachnological Society notes that the spider may bite if it is roughly handled and describes the bite as painful, similar to a bee sting. The Spiders of Europe database adds that the reports of bites to people are old and unverified, and that no recent verified case has been published.
The simplest approach is not to pick one up. If anyone develops a severe or worsening reaction after a suspected bite from any spider, they should seek medical advice. Our spider bites and safety section explains how to think about spider bites in general.
Other spiders called “water spiders”
Many spiders live near water, and several are commonly called water spiders. The most familiar are the fishing spiders, which are a separate group from Argyroneta.
- Fishing spiders (Dolomedes). These large hunters occur on several continents. Many species sit at the edge of ponds and streams with their front legs resting on the surface, feeling for ripples made by prey. Some species also live away from water, in wooded areas.
- Australian water spiders. The Australian Museum uses “water spiders” as a name for a group of Australian nursery web and fishing spiders. One example is Megadolomedes australianus, a large species recorded in New South Wales. The World Spider Catalog now places Dolomedes and Megadolomedes in the family Dolomedidae; older guides list them under Pisauridae.
These spiders can run across the water surface, and some can dive for a while, breathing from a thin layer of air held by their body hairs. But they do not build an underwater air bell and do not live underwater the way Argyroneta aquatica does. If you are trying to work out which spider you have seen, location is the first clue. You can browse other groups on our spider types page.
| Feature | Water spider (Argyroneta aquatica) | Fishing spiders (Dolomedes, Megadolomedes) |
|---|---|---|
| Where it spends its time | Mostly underwater | Mostly on plants, banks or the water surface |
| Air supply underwater | Air-filled silk bell | Short dives using air held by body hairs |
| Native range | Europe and temperate Asia | Many regions, depending on the species |
| Family (World Spider Catalog) | Argyronetidae | Dolomedidae |
Frequently asked questions
Is the water spider the same as the diving bell spider?
Yes. Both names refer to Argyroneta aquatica. “Diving bell spider” comes from the air-filled silk bell it builds underwater.
Do water spiders live in North America?
Not the diving bell spider. Its native range covers Europe and temperate Asia. Spiders called water spiders in North America are usually fishing spiders in the genus Dolomedes.
How long can a water spider stay underwater?
For most of its life. It breathes air stored in its bell, and research suggests the bell can draw in enough oxygen from the water that, in some conditions, the spider may need to add fresh air only about once a day.
Can a water spider live out of water?
It does leave the water occasionally, for example to collect air at the surface, and some sources report that it moults out of the water. But it is adapted to life underwater and depends on clean, plant-filled fresh water.
References
- World Spider Catalog. Argyroneta aquatica (Clerck, 1757). Natural History Museum Bern. Accessed October 2026. wsc.nmbe.ch/species/8306
- World Spider Catalog. Megadolomedes australianus (L. Koch, 1865). Natural History Museum Bern. Accessed October 2026. wsc.nmbe.ch/spec-data/34050
- Nentwig W., Blick T., Bosmans R., Gloor D., Hänggi A. & Kropf C. Spiders of Europe: Argyroneta aquatica. Accessed October 2026. araneae.nmbe.ch/data/201
- Seymour R.S. & Hetz S.K. (2011). The diving bell and the spider: the physical gill of Argyroneta aquatica. Journal of Experimental Biology 214: 2175–2181. doi:10.1242/jeb.056093
- Schütz D. & Taborsky M. (2003). Adaptations to an aquatic life may be responsible for the reversed sexual size dimorphism in the water spider, Argyroneta aquatica. Evolutionary Ecology Research 5: 105–117. Abstract
- Mammola S., Cavalcante R. & Isaia M. (2016). Ecological preference of the diving bell spider Argyroneta aquatica in a resurgence of the Po plain (Northern Italy). Fragmenta entomologica 48(1): 9–16. doi:10.13133/2284-4880/158
- British Arachnological Society. Spider and Harvestman Recording Scheme: Argyroneta aquatica summary. srs.britishspiders.org.uk
- British Arachnological Society. Water spiders. britishspiders.org.uk/node/26498
- The Wildlife Trusts (Wildlife Watch). Water spider. wildlifewatch.org.uk
- Australian Museum. Water spiders. australian.museum
- Penn State Extension. Fishing spider. extension.psu.edu/fishing-spider
