When I nudged a spider, it immediately abseiled to the floor. How did it make a strand of web so quickly, or do spiders have an emergency escape kit in their bodies? When they land, do they cut the cord?
Jane Lambert Penzance, Cornwall, UK
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Watching a spider on a window, I saw it immediately drop like a stone to a ledge when the window was nudged, apparently under the influence of gravity.
A minute later, the spider did the whole thing in reverse, ascending to its original position at exactly the same speed at which it had descended. So it seemed that the speed of descent wasn鈥檛 dictated by gravity after all.
Todd Blackledge University of Akron, US
When a spider falls or jumps from a height, it already has a built-in safety line attached. Most spiders continuously spin a dragline of silk as they move around and periodically secure that line with small attachment discs of adhesive silk to catch any fall 鈥� just like a rock climber鈥檚 karabiner.
The dragline rapidly pays out from one of many silk glands on the spider鈥檚 spinneret and is produced from a pre-made stockpile of liquid silk 鈥渄ope鈥� stored inside the gland.
This liquid passes through an S-shaped duct that processes it into solid silk fibre in milliseconds through a combination of shearing of the liquid silk, removal of water and a drop in pH. You can think of the silk as 鈥渓iking鈥� to exist in two different states: as a liquid solution in the gland and as a solid fibre in any other chemical environment 鈥� but nothing in between. The 鈥渟pinning鈥� of the fibre simply involves the silk being nudged from one physical state to the other.
Many spiders have a muscular valve at the end of the spinning duct that can clamp down on the dragline to slow, or even stop, the spider鈥檚 descent. Thus, the spider can stop almost on a dime in mid-air, then continue to descend.
After reaching the ground or some other perch, the spider rapidly secures its dragline with another attachment disc, in case of another fall, and continues trailing its safety line.
Spiders do sometimes cut silk threads, but usually only as part of the process of building or utilising webs. Draglines are almost never cut. That is why you can often see hundreds of silk threads criss-crossing your bushes or lawn in the early morning light 鈥� evidence of the nightly wanderings of many spiders.
Fritz Vollrath University of Oxford, UK
Spiders produce their silk 鈥渙n the hoof鈥� by spinning stored liquid silk into a thread at speeds of up to a metre a second. Jumping spiders can do it even faster.
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