Spiders shoot silk safety lines from their feet

15 May 2011


Scientists have solved a spidery controversy and shown that tarantulas shoot silk from their feet to stop themselves falling off steep, slippery surfaces - just like Spiderman himself.

Back in 2006, a paper in Nature suggested that tarantulas have this safety measure up their sleeves to save themselves from a potentially fatal fall - after all they are big creatures weighing up to 50g.  But another group of scientists refuted the study, claiming there is no evidence of silk coming out of the giant spiders' feet.

Chilian Rose Hair TarantulaNow Claire Rind and colleagues from Newcastle University, publishing in the Journal of Experimental Biology, decided to dig into this spidery mystery by putting Chilean rose tarantulas into a glass aquarium tank and watching how well they can cling to a smooth, vertical wall.  Turns out they can hang on well, although they occasionally slip.  And they do indeed leave behind silky footprints as identified under a microscope.

To find out where the silk was coming from, the team filmed the tarantulas repeatedly on the vertical glass wall and picked out times when only their feet touch the glass and no other part of their body. When that was the case, there was still silk left on the glass.

But, the question is, where on their feet is the silk coming from exactly? Rind had a pet Mexican flame-knee tarantula - called Fluffy - when she was younger and kept all its moulted exoskeletons.  Examining these and the exoskeletons of other tarantulas under an electron microscope revealed tiny spigots or nozzles that produce silk sticking out from miniscule hairs all across their feet.

And it turns out these nozzles could be something of a "missing link" between the modern web-makers and ancient spiders. The patterns of the tarantula's nozzles resemble those of an extinct species Attercopus - this is a proto-spider from 386 million years ago and is the oldest-known silk-producer.  The feet nozzles look similar to sensory hairs that cover the entire body - so they could be an intermediary evolutionary step between hairs and silk-producing nozzles.


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