How tarantulas hold on tight

Fluffy the tarantula has resolved the argument about how the arachnid stays secure on a vertical surface and may have revealed the missing link between the first silk-producing spiders and their modern counterparts.

Tarantulas shoot safety silk from their feet to prevent their falling from a vertical surface

Tarantulas – unlike other spiders – struggle with vertical surfaces and Dr Claire Rind from Newcastle University discovered that the arachnids shoot silk safety threads from their feet to stay secure.

“The animals are very delicate,” said Rind. “They couldn’t survive a fall from any height.”

Rind and undergraduate student Luke Birkett tested how well three ground-dwelling Chilean rose tarantulas kept their footing on a vertical surface. A spider was placed in a very clean aquarium containing microscope slides on the floor. They upended the aquarium to see if the spider could hang on – shaking it gently if the spider didn’t fall.

“Given that people said tarantulas couldn’t stay on a vertical surface, we didn’t want to find that they were right,” Rind said.

The tarantulas slipped, but quickly regained their footing – analysis of the microscope slide where the spider stood before slipping showed minute threads of silk attached. To prove the source of the silk was the feet, Rind filmed the spiders as they were rotated vertically – the arachnids only produced their safety thread then they slipped.

Next was to identify exactly where on the feet the silk came from. Rind – a keen arachnologist – collected all the moulted exoskeletons of her Mexican flame knee tarantula, Fluffy, when she was younger and examined them under the microscope. She discovered minute threads of silk protruding from microscopic hairs on Fluffy’s feet.

She also examined moults from the Chilean rose and Indian ornamental tarantula and found minute reinforced silk-producing spigots. These three species are only distantly related, so Rind deduced all tarantulas probably produce these life-saving threads.

The scientists realised that tarantulas could be the missing link between the first silk-producing spiders and modern web spinners. The spread of spigots of the tarantula’s foot is similar to those on the abdomen of the first silk spinner, the extinct Attercopus from 386 million years ago.