A thin coating of oil on the surface of the spider’s legs prevents them from sticking to their own web.
Spiders have 3 pairs of spinnerets (silk spinning apparatus) located beneath the hind tip of their abdomen. Silk, made up of proteins, secreted by the silk glands, and are made into fibres as thin as a thousandth of a millimetre. The threads we see are actually a bundle of these fibres. The proteins are water soluble when secreted, but when made into a fibre, some Physical and chemical changes take place, and so, after a while the fibre becomes tough and does not dissolve in water. In fact, it becomes stronger than a steel wire of the same thickness. Hence, the spider silk is also used to make bullet proof vests.
To construct a web, the spider first lays the radical threads. These resemble the spokes on a wheel and they radiate from the centre or hub of the web. The radial fibres are then connected by spiraling threads. There may be 10-60 turns in a web. To capture the insects, spiders scatter small glue droplets throughout. The glue droplets remain sticky by absorbing moisture from the air. They also increase the capacity of the web to resist wind forces.
While some spiders do not place glue droplets around the central area of their web so that they can wait there for the prey, a few others attach a separate ‘signal thread’ from the web’s centre to a nearby place (not on the web) where it can conveniently relax. When the insects get stuck to web, spiders sense the vibrations and leap on the prey.
To help avoid being caught in their own webs, the spiders secrete oil and coat it on their toes. One can test this by dipping a spider’s legs in ether, an organic solvent, which dissolves the oil. If the spider is returned to the web after the dip, it will be caught in its own web.
