Tuesday, 7 February 2012

The Bolas spider

Gaucho cowboy spiders in our grassland

A particular type of lasso, known as Bolas (or boleadoras, balls) has been used since Pre-Columbian times to capture wild animals, and is still used nowadays by Gauchos, or South American cowboys, to lasso cattle. It comprises three or more heavy balls at the end of three joined cords that is spun above the head and then thrown to entangle itself around an animal's legs to bring it down.

Ivory and silver Gaucho bolas

There is a grassland-dwelling spider that does the same thing... As David Attenborough breathlessly explains, the bolas spider hangs from a line of silk, emitting a pheromone tailored to attract a particular moth of its choice, then snares its prey with its spinning web-made bolas.   

John Roff, who discovered a new species of bolas spider in the grassland area of our local botanical gardens (Pietermaritzburg, SA), describes its deft action:  

"The spiders first constructs a few silk lines, known as trapeze-lines, from which they hang using their hind legs. A short silk thread, the bolas-line, is then constructed, with from one to several sticky globules (bolas) fixed to the free end. The bola consists of a large globule of gluey mass containing a mass of fibres . The bolas-line is rotated (with a second pair of legs), catching prey, usually moths in flight."

Here is the local bolas spider in action (video thanks to Charlene Russell, WESSA)


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