Intertidal spiders are playing on hard mode
Bec Crew is a Sydney-based science communicator with a love for weird and wonderful animals. From strange behaviours and special adaptations to newly discovered species and the researchers who find them, her topics celebrate how alien yet relatable so many of the creatures that live amongst us can be.
Spiders are perfect little machines, built for a life of stealth and agility, whether they take up residence in gardens, forests, grasslands or inside our homes. Some spiders have managed to verge close enough to the water’s edge to snag a fish meal, but it’s those that have adapted to a waterlogged existence that have well and truly turned up the difficulty on life.
Intertidal spiders (family Desidae) live on the coast, navigating low and high tides, day in, day out. There are many genera spread around the world, but the vast majority are found in Australia and New Zealand (because of course we’d be the global hub of beach spiders).
Some, known as marine spiders (genus Desis), are so conditioned to the water, they can move into an empty barnacle shell or tubeworm burrow, seal up the entrance with silk and float on the high tide. The silk seal creates an air bubble, which can sustain the spider while its makeshift home bobs below the surface, buffeted by the waves.
A great example of this behaviour is Desis marina, found in New Zealand, New Caledonia and the Chatham Islands. A tiny, 8 mm-long nocturnal spider, D. marina can stay submerged in its seashell home for up to 19 days, aided by the fact that it has one of the lowest respiratory rates among spiders.
Then there’s Desis bobmarley, even smaller at 6 mm-long, named after Bob himself. It was discovered just three years ago on the Great Barrier Reef, living among the brain corals, which provide the perfect camouflage.
As Barbara Baehr from the Queensland Museum, one of the researchers who discovered D. bobmarley, told Australian Geographic in 2018, the species uses the long hairs on its legs and abdomen to create an air bubble around its body to help it breathe underwater.
“During high tide these extremely rare and unusual animals hide in the air chambers, but during low tide they are vagrant hunters found on corals, barnacles or debris,” said Baehr.
The spider pictured above is Desis formidabilis, feeding on sea lice on the shore in South Africa.
Formidable in name and in life, this spider has opted to live in crevices under boulders on rocky shores, constantly dealing with the lapping tide. Its relatives on the land must be counting their lucky stars for all their dry legs.
Here’s some fantastic footage of D. marina scurrying around in its natural habitat, which is something to keep in mind next time you’re barefooting around the rockpools…