A researcher in Britain says she's settled a long-running debate over how tarantula spiders manage to climb walls and hang upside down - seemingly impossible tasks for the big, heavy arachnids.
Her study has confirmed that tarantulas can shoot sticky threads of silk from microscopic spigots on the bottom of their feet to prevent a potentially deadly tumble. Even a short fall that would not harm the average web-spinner would likely spell death for the hefty, fist-sized tarantula, a ground-dweller that can weigh as much as 50 grams.
Like many other spiders, tarantulas have silk-producing organs called spinnerets located on their abdomens. Rather than spinning webs, the giant land spiders use their silk to line or guard their underground burrows. They have also been known to build hammock-like structures for a cozy place to spend the day.
Scientists have long believed that tarantulas grabbed silk from the spinnerets to secure their grip on vertical climbs. But in recent years, experts have speculated that the sticky silk was actually coming from the spiders' feet. Biologist Claire Rind of the University of Newcastle decided to take a closer look. Examining naturally-shed tarantula exoskeletons with a high-powered electron microscope, Rind was able to detect tiny silk-producing spigots protruding from the hairs covering the spiders' eight furry feet. In experiments with live spiders climbing the walls of a glass terrarium that was then tipped on its side, she also observed that the weight-conscious arachnids only produced safety silk from their feet when they felt themselves slipping.
The researcher says the tarantula's ability to spin silk from its feet suggests it could be an evolutionary link between the first silk-spinning spiders 386 million years ago and their modern web-making ancestors.
The University of Newcastle scientist made the same finding in three geographically remote species of tarantulas she studied - the Chilean Rose, the Indian ornamental, and the Mexican flame-kneed. Given the diversity of the three species, Rind believes it is likely that all tarantulas have the ability to shoot safety-silk from their feet.
The study will appear in the June edition of the Journal of Experimental Biology.