Curious Kids: can spiders swim?

Can spiders swim?

Waubra Preschool students, Victoria, Australia

What a great question!

Most spiders don’t swim by choice. But they sure can survive in water when they need to. From floating like a boat, to paddling like a rower, to carrying their own scuba bubbles, spiders have developed brilliant ways to deal with water.

Let’s dive into the science in some more detail, and look at how spiders handle getting their paws wet, with examples from our local bush.

Spiders can run across water

Water has surface tension – this acts like a kind of invisible skin that can hold up small, light objects.

Many spiders are tiny and have water-repellent hairs on their legs, so they can stand or run on water without sinking.

For example, fishing spiders wait at the water’s edge and scuttle across the surface to grab insects, tadpoles or even small fish.

If prey escapes underwater, this spider can even hide beneath the water’s surface briefly, then come back up.

Spiders can hold their breath underwater for days

Spiders don’t have gills, so they can’t get oxygen from water like fish do. But they have evolved clever strategies for staying alive if they stay in the water for a long time.

For example, the Australian Sydney funnel-web spider often falls into backyard swimming pools. People might see one and think it drowned, but it can actually survive underwater for hours by holding its breath much longer than a human could.

That’s because it breathes much more slowly than we do. Like many spiders, it has both tracheae (tiny air tubes) and book lungs (they look like a book with many pages) for breathing. Some spiders can close these and become watertight, to hold their breath for a long time.

Some trapdoor spiders have been recorded only taking a breath every six minutes.

Do not burst their bubble

Some spiders take the air with them like a scuba diver.

On the Great Barrier Reef coast, a little intertidal spider called Desis bobmarleyi actually lives part of its life under seawater. At high tide, it hides in a silk-lined air pocket in coral or shells. It uses the long hairs on its legs and body to trap a bubble around itself so it can breathe underwater between the tides. When the tide goes out, this spider comes out to hunt on the wet reef.

And in other parts of the world, there’s the famous diving bell spider, the only spider that spends its whole life entirely underwater.

It weaves an underwater silk web that it fills with air – like an underwater house. This spider can stay underwater for more than a day at a time by letting its air-bubble vessel actively pull oxygen from the water.