Page 76 - The Miracle in the Spider

4 MICRONS
100 NANOMETRES 20 NANOMETRES
Enlargement of spider thread (a) shows it to be a composite material
made of strands of disordered amino acid chains and ordered
crystals (b and c). Each crystal is made up of different-size amino
acid groups pressed into an accordionlike formation, called beta-
pleated sheets (d). The surrounding strands are called alpha helixes;
their contracted disarray provides silk with its elasticity. When silk is
emitted, shearing forces like those shown at the right (e) are applied
to some alpha helixes. Consequently, their hydrogen bonds break
and they become beta-pleated sheets. (f), as the similarity of the
highlighted molecular strands shows. (1 nanometre= 0.000000001
meter).

apparently reinforce the frame and dragline silks; cocoon silk; a silk to
wrap captured prey; and a silk to attach the frame and dragline silks to
the substrate. 24
These silks, in the same way as they have different qualities from the
point of view of strength and elasticity, also exhibit different thicknesses
and levels of stickiness. For example, although the dragline, which plays
such a large part in the spider's life, does not possess the quality of
stickiness, it is nevertheless strong and elastic. It can easily bear weights
up to two or three times the weight of the spider. It is thanks to this silk
that the spider, carrying the prey it has caught, can move safely up and
down.
As we have seen, in order to live, the spider needs to be able to
produce different types of silk and also to know where to use each one.