Spiders’ silk is an amazingly strong material
SPIDERS and this time of year sit well together, and any mention of spiders brings silk to mind. As autumn draws in and nights grow colder and longer, spider webs become more obvious on cool mornings especially when their intricate constructions are bedecked with dozens of tiny, glistening droplets of dew.
As the day warms up, the night-time dew evaporates and the spider webs fade into insignificance for all but the few who pause to marvel at their often elaborate construction.
Not all spiders spin silken webs. Some, like the wolf spiders, are active hunters who use stealth and speed when out looking for food. When a potential meal is spotted they pounce on their prey and inflict a killer bite. Others, like the crab spiders, use concealing camouflage and lie in ambush in flowers, their colour matching the colour of the petals, waiting for dinner to come to them.
The silk-spinners use a variety of tactics to trap prey. Some spin an untidy tangle of silk, others construct tunnels and silken tubes. Yet others spin the flat orb webs, spiral wheel-shaped constructions in the vertical plane, sometimes as big as a dinner plate.
Spider silk starts off life as a liquid. When it is drawn out it forms a protein fibre. The grands that extrude the silk are internal; the visible part on the surface at the rear end of the spider’s body is the spinneret. Spinnerets normally occur in pairs and, depending on the species involved, silk-spinning spiders can have as few as two or as many as eight spinnerets.
While we tend to think of spider silk as a single substance, spiders can spin up to seven different kinds of silk and they use these different silks, and various combinations of them, for a host of different purposes.
Dragline silk, one of the seven different types of spider silk, is reported to be as strong per unit weight as steel, but much tougher. A Garden Spider on a branch may drop to the ground below on a strand of dragline silk. In addition to using it as a safety line, the spider uses dragline silk to construct the outer frame and spokes of its orb web.
Dragline silk adds strength to the web, but it is useless for catching prey. The silk that is spun to catch prey is also tough like dragline, but it differs in being very sticky and extremely elastic and stretchy.