Diving Bell (Argyroneta aquatica)
Argyroneta aquatica is the only spider on Earth that spends its entire life below the surface of fresh water. It builds a dome of silk between water plants, fills it with air carried down on its body, and lives inside that bubble — hunting, moulting, mating and raising young in a pocket of air that also works as a gill, quietly pulling oxygen out of the pond around it.
By Dr Richard J. Pearce (PhD)Published May 22, 2019Updated September 13, 2026✓ Reviewed by Dr. James Watuwa
In this guide
Physical description and identification
Out of water the diving bell spider is unremarkable: a medium-sized, brownish, thickly haired spider that could pass for a small wolf spider. Underwater it is unmistakable. Air trapped by dense, water-repellent hairs coats the abdomen and legs and turns the animal into a moving bead of mercury — no other spider is ever seen swimming and glinting in open water.
Classification has moved around. The species was long placed in a family of its own, Argyronetidae, then in Cybaeidae, and is currently treated as a member of Dictynidae.
Adults
- Size: males measure roughly 10–15 mm in body length and females 8–12 mm. Males being the larger sex is genuinely unusual among spiders and makes Argyroneta a textbook case of reversed sexual size dimorphism.
- Colour: light to dark grey-brown with a velvety abdomen. Submerged, all of it is hidden under the silvery air film.
- Legs: long and strong, the third and fourth pairs fringed with stiff bristles that work as paddles. Males have longer, more slender front legs and swim faster.
- Hairs: fine hydrophobic setae hold a permanent film of air, the plastron — what the spider carries down to inflate the bell and what supplies its book lungs while it swims.
- Eyes: eight small eyes in two rows, none enlarged. See our guide to spider eyes.
Eggs and egg sac
The female partitions off the upper part of her bell with a wall of silk and builds her egg sac inside that chamber, the driest and most oxygen-rich part of the structure. A clutch holds roughly 30 to 70 eggs. She guards it from the lower half of the same bell, and because the bell is a physical gill she can stay with the eggs for long periods without surfacing.
Spiderlings
The spiderlings hatch inside the maternal bell and remain there for a short time only. Within days to a couple of weeks they leave and each builds its own miniature bell nearby — they do not stay with their mother until maturity, as is sometimes claimed. Juveniles moult inside their bells: a freshly moulted spider is soft and its new hairs must dry before they will hold air. See spider molting and the spider life cycle.
The web — the diving bell
The bell is a sheet of dense silk spun between the stems of submerged plants and shaped like an upturned thimble. The spider then makes repeated trips to the surface, each time breaking the surface film with its abdomen and hind legs, trapping a bubble against the plastron and releasing it under the silk until the dome inflates.
What happens next is why the species is famous. The wall of the bell is permeable to gas, so the air pocket works as a physical gill: as the spider consumes oxygen the partial pressure inside falls below that of the water, dissolved oxygen diffuses in across the silk and carbon dioxide passes out. Nitrogen slowly leaks away, so the bell deflates and has to be topped up — but in cool, well-oxygenated water a resting spider may surface only about once a day. The popular claim that the bell works best in stagnant water gets this backwards: gas exchange runs on the oxygen gradient, so in warm, oxygen-poor water the gradient collapses and the spider must surface far more often. See our guide to spider webs.
Where diving bell spiders live
Argyroneta aquatica is a Palaearctic species. It occurs across most of Europe, including the British Isles — see spiders in the UK, Ireland, France, the Netherlands, Poland and Finland — and extends east through Russia and Siberia to Japan, Korea and northern China, with southern outposts in the Caucasus, Turkey and Iran. It is not native to the Americas, Africa or Australia and has not been introduced anywhere.
The habitat is specific: clean, still or very slow-moving fresh water with dense submerged vegetation. Ponds, ditches, fen pools, canals and sheltered lake margins all qualify; fast rivers and bare, silted water do not. The plants are not optional — the bell must be anchored, and the spider needs cover from fish.
That dependence makes it vulnerable. Wetland drainage, nutrient enrichment that strips oxygen from the water, and the loss of clear weed beds have caused declines across much of western and central Europe, and the species appears on several national red lists.
Are diving bell spiders venomous?
Yes, like almost all spiders. Argyroneta aquatica uses venom to kill the aquatic invertebrates it catches. In human terms it is not medically significant: no antivenom exists, none is needed, and there is no record of a serious systemic reaction or lasting injury from this species.
It does have relatively long chelicerae for its size, an adaptation for gripping struggling prey underwater, and they pierce human skin cleanly. That is why a bite from this otherwise harmless spider hurts more than its size suggests. It is unrelated to the recluse spiders and the widow spiders and shares none of their venom chemistry.
Can diving bell spiders bite?
They can, and they are among the few small spiders willing to do it when handled. Encounters are rare simply because the spider lives underwater — most recorded bites involve people who scooped one out in a pond net, or aquarists and researchers handling specimens.
A bite is genuinely painful out of proportion to the spider's size, a sharp burning sting at the puncture. Local redness, swelling and inflammation follow and usually settle within a few days. A minority of reports mention mild systemic effects such as slight fever or nausea, which resolve on their own. Wash the site, apply a cold pack, keep the limb still and take an ordinary painkiller. No cutting, sucking or home remedy is appropriate. See a doctor if pain keeps escalating, the redness spreads and the area turns hot, or symptoms appear away from the bite.
Do not confuse it with a fishing spider. Fishing spiders and nursery web spiders such as the dark fishing spider hunt on the surface film and dive only briefly. They are far larger, with long sprawling legs and a flat posture on the water. A spider living beneath the surface inside a silver bubble of air, in Europe or northern Asia, can only be Argyroneta aquatica.
Ecological importance and behavior of the diving bell spider
The diving bell spider is an active underwater hunter rather than a web-trapper. It leaves the bell, clambers through the weed on its bristled legs and seizes prey directly: mosquito and midge larvae, mayfly and damselfly nymphs, water boatmen, freshwater shrimps and occasionally fish fry or tadpoles. Prey is carried back to the bell and eaten in the air pocket, because feeding underwater would flood the mouthparts.
Natural predators: fish are the main threat — sticklebacks, perch, roach and anything that hunts in weed beds — along with frogs, newts, dragonfly nymphs, diving beetles and water birds. The bell offers real protection, and retreating into dense vegetation is the spider's main defence.
Prey-predator dynamics: by taking mosquito and midge larvae in quantity, a healthy population sits directly on the insect stages that produce biting swarms, in a layer of the pond most predators cannot reach. It is also a useful indicator species: because it needs clear, oxygen-rich, weedy water, its presence is a fair sign of a pond in good condition.
Seasonal behaviour: adults are active from spring through autumn. Mating happens underwater, and unusually for spiders the male is the larger animal and courtship is comparatively peaceful — he enlarges his bell beside the female's, spins a connecting tunnel and mates inside. In autumn the spiders build thicker-walled overwintering bells, sometimes inside empty snail shells, seal them and sit out the cold. Adults live around two years, longer than the single year often quoted.
Relationship with humans: almost none. The species is shy, restricted to clean water and declining, so the practical relationship is conservation rather than control: keep ponds clean and weedy, and do not handle one if you net it.
Similar spiders and how to tell them apart
| Spider | How it differs from the diving bell spider |
|---|---|
| Fishing spiders (Dolomedes) | Much larger, with a flat sprawling posture on the surface film. They walk on water and dive only to escape or grab prey; they never build an underwater air bell. |
| Dark fishing spider | A North American Dolomedes with strong chevron markings, often found well away from water on tree trunks and house walls. |
| Six-spotted fishing spider | Pale stripes along the carapace and rows of white spots beneath the abdomen. A surface hunter of North American pond margins. |
| Nursery web spiders (Pisauridae) | The family containing the fishing spiders. Females carry the egg sac in their jaws and build a nursery tent in vegetation above water, not a dome beneath it. |
| Wolf spiders (Lycosidae) | Two large forward-facing eyes in a three-row pattern, and females carry the egg sac on the spinnerets. Some run across water but none lives in it. |
| Other Dictynidae | Otherwise tiny cribellate mesh weavers on plant tips and rock faces, a few millimetres long and entirely terrestrial. |
Quick facts
| Other names | Water spider, European water spider |
|---|---|
| Distribution | Europe including the British Isles, east through Russia and Siberia to Japan, Korea and northern China, with outposts in the Caucasus, Turkey and Iran. |
| Habitat | Clean, still or slow-moving fresh water with dense submerged weed: ponds, ditches, fens, canals and sheltered lake margins. |
| Diet | Mosquito and midge larvae, mayfly and damselfly nymphs, water boatmen, freshwater shrimps and occasional fry or tadpoles. |
| Lifespan | About two years, overwintering in a sealed, thick-walled bell. |
| Predators | Fish, frogs, newts, dragonfly nymphs, diving beetles and water birds. |
| Web | A silk dome anchored to water plants and filled with air from the surface; it functions as a physical gill. |
| Conservation | Declining across western and central Europe through wetland drainage and nutrient pollution; red-listed in several countries. |
Did you know?
- The genus name comes from the Greek argyros, silver, and a root meaning to spin — "silver spinner", after the mercury-like sheen of the trapped air layer.
- The bell is not just a store of air, it is a working lung. Measurements inside real bells show dissolved oxygen diffusing in from the pond, so a resting spider in cool water can stay down for around a day on one filling.
- Because gas exchange depends on the oxygen gradient, warm stagnant water is the worst case, not the best — one reason the species disappears from polluted and weed-free ponds.
- Males are the larger sex, reversing the usual spider pattern. The leading explanation is that they range widely to find females, so a larger, longer-legged body dives and hunts better, while a smaller female uses less oxygen sitting in her bell.
- Everything happens inside the air pocket: feeding, moulting, mating, egg-laying and overwintering. The spider enters open water only to hunt, to swim between bells and to fetch more air.
In summary, the diving bell spider is a fully terrestrial animal that solved life underwater without changing its basic anatomy — it simply took its atmosphere with it. It is harmless beyond a painful bite if handled, it eats mosquito larvae by the hundred, and it survives only where fresh water is still clean enough to hold both oxygen and weed.
Frequently asked questions about the diving bell spider
How does the diving bell spider breathe underwater?
It spins a dome of silk between water plants and fills it with air carried down on its body. The silk wall is permeable to gas, so as the spider uses oxygen more diffuses in from the pond and carbon dioxide passes out. The bell works as a physical gill and only needs topping up as nitrogen slowly leaks away.
Why does a diving bell spider look silver underwater?
Dense water-repellent hairs on the abdomen and legs hold a permanent film of air called a plastron. Light reflecting off the boundary between that air layer and the surrounding water produces a bright mirror-like sheen, which is where the genus name Argyroneta, meaning silver spinner, comes from.
Are male or female diving bell spiders bigger?
Males are larger, which is unusual among spiders. Males reach about 10 to 15 millimetres in body length and females about 8 to 12 millimetres, and males also have longer, more slender front legs. The likely reason is that males swim and range widely, so size aids diving and hunting.
What happens if a diving bell spider bites a person?
The bite is sharply painful for the spider's size because the chelicerae are long, and it causes local redness, swelling and inflammation that settle within a few days. A few reports mention mild fever or nausea that resolves on its own. Wash the site, use a cold pack and see a doctor if symptoms spread.
What is the diving bell spider's web used for?
The air-filled dome is the spider's home rather than a trap. It eats, digests, moults, mates, lays eggs and overwinters inside it, because all of those need a dry, air-filled space. Prey is caught in open water and carried back to the bell to be consumed.
How many eggs does a female diving bell spider lay?
A clutch holds roughly 30 to 70 eggs. The female walls off the upper section of her bell with silk and builds the egg sac in that chamber, the driest and most oxygen-rich part of the structure, then guards it from the lower half of the same bell.
Where in the world do diving bell spiders live?
Across Europe including the British Isles and east through Russia and Siberia to Japan, Korea and northern China, with outposts in the Caucasus, Turkey and Iran. They need clean, still or slow-moving fresh water with dense submerged weed, such as ponds, ditches, fens and canals.
Is the diving bell spider the only spider that lives underwater?
Yes. Argyroneta aquatica is the only spider known to spend its whole life submerged. Some other spiders survive immersion or hunt at the surface, and a few intertidal species seal themselves in air chambers between tides, but none lives permanently beneath fresh water the way this one does.
How long do diving bell spiders live?
About two years. Adults are active from spring through autumn, then build a thicker, sealed overwintering bell — sometimes inside an empty water snail shell — and pass the cold months at a low metabolic rate, occasionally under ice, emerging again when the water warms.
Are diving bell spiders rare or endangered?
They are not globally endangered but have declined markedly across western and central Europe and appear on several national red lists. The causes are wetland drainage, nutrient pollution that strips oxygen from the water, and the loss of the clear, weedy ponds the species depends on.
References
- World Spider Catalog (2026). Argyroneta aquatica (Clerck, 1757). Natural History Museum Bern. wsc.nmbe.ch/spec-data/14930/taxon
