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Madagascar's elusive shell-squatting spider filmed

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Sir David Attenborough describes the fascinating behaviour of the spider Olios coenobitus

An elusive spider that lives in snail shells suspended from bushes has been caught on camera by a BBC film crew.

Olios coenobitus was first discovered in 1926 but few studies have been made of it in the wild since.

New footage reveals how the spiders hoist snail shells off the ground using silk threads and shelter inside them.

The team filming for BBC Two series Madagascar believe this is the first footage to show how the spiders protect themselves from predators.

O. coenobitus are known to live in thorny succulent bushes in the south of Madagascar.

In the 1960s, French scientists studied the spiders in captivity and recorded their unique home-building method.

Researchers observed the spiders hoisting snail shells many times their own weight off the ground using a network of silk threads.

The captive spiders raised snail shells up to 8cm from the floor in order to shelter inside them.

However, anecdotal evidence suggested that in the wild the spiders' aerial homes reached much grander heights.

Photographs taken by keen-eyed amateur naturalists showed snail shells suspended much higher in bushes.

However, few studies have been made of the animals in the wild and this home-building behaviour remained unconfirmed by scientists.

A BBC film crew working on new series Madagascar were determined to film the spiders in action.

Field assistant Jonathan Fiely scoured the south of the island in search of the spider.

It was a real hold your breath moment the first time the spider peeked out of its shell! Jonathan Fiely

Speaking to local people, the biologist learned that they collected the spiders from the shells to feed their chickens.

Children in the area joined in the search for the spiders but once they had located them, the crew were faced with a further challenge.

The home-building adult spiders were only active at night and extremely sensitive to light.

"The first time we attempted film we we tried using lights, but this was a no-go as far as the spiders were concerned," explained Mr Fiely.

The team resorted to more sophisticated technology, using infrared lights and cameras to capture the unique behaviour.

"The slightest vibration would send the spider deeper into its shell, but with patience and persistence we witnessed the first emergence."

"It was a real hold your breath moment the first time the spider peeked out of its shell!" Mr Fiely told the BBC.

SPIDER FACTS Spider silk is as strong as steel but weighs far less. Spiders live in every habitat on earth except the polar regions. Scientists have recorded over 500 species of spider in Madagascar. Find out more about Madagascar's unique wildlife

The footage revealed the spiders' fascinating technique, spinning silk to hoist empty snail shells up to 50cm off the ground.

"With almost flawless precision the spider descends on a single line of silk from the branch and attaches its first thread to the shell," said Mr Fiely.

"This is the critical anchor the spider uses, as it attaches a new thread to the shell, ascends to the branch again, and winches the shell up."

The filmmakers watched as this process was repeated, sometimes with further anchor threads added to stop the shells spinning in the breeze.

The spiders made significant effort to avoid predators, hauling shells up to 20 times their own weight for over half an hour.

"Just hiding in a shell on the ground would expose the spider to heat and ants, which are voracious predators of the desert ecosystem," said Mr Fiely.

With so few previous studies of the spiders' behaviour, the team believes this footage could be the first to reveal their unusual technique in full.

"Madagascar is one of the few places left in the world where you can still seek out and film new species and new behaviour," said series producer Mary Summerill.