Nature & Beasts
Why does a spider not stick to its own web?
- Only some threads are sticky, and it walks the others
- Its legs are oiled
- It never touches the web
The answer is Only some threads are sticky, and it walks the others. The spiral is sticky, the spokes are not, and it walks the spokes.
Mostly because only part of the web is sticky. An orb web has non-sticky radial spokes running out from the centre and a sticky spiral wound between them, and the spider walks the spokes. When it must cross the spiral it does so carefully, and it can still get caught if it is careless.
There is more to it than route-planning. The legs are covered in a fine coating that reduces adhesion, the tips carry stiff bristles that minimise how much surface actually touches the thread, and the spider grooms its legs regularly - a spider whose legs are washed with a solvent sticks to its own web.
The glue itself is a marvel of engineering: droplets of a sticky polymer strung along an elastic core, which stay tacky for days and absorb humidity from the air to stay that way. Spider silk is also stronger than steel by weight and far tougher, and dozens of attempts to farm or synthesise it have mostly failed - spiders are cannibals and cannot be kept in numbers, so the current approach is to put the genes into goats, bacteria or silkworms.