Spider
Silk
Spiders’
silk spinning organs are called "spinnerets". Each
spinneret has numerous silk outlets, called "spigots".
Both spinnerets and spigots can be many different shapes and
sizes and produce several different types of silk.
When
liquid silk is extruded from the silk glands (controlled by
internal pressure changes, muscular valves, and external pulling),
it is forced through the narrow exit channel of a spigot and
the silk molecules are physically re-arranged to produce a solid
silk line.
A
silk line gets its elasticity from its spring-like chain structure
of molecules that stretches when pulled. Its strength comes
from pleated molecules that form hard, crystalline ‘bricks’
within the line.
The
Carrai Cave Spider uses enlarged claws on its front legs to
scoop up living prey, such as guano moths and beetles, onto
a woolly silk ‘platform’ which immediately wraps tightly
around it.
Web
spinning spiders rely on vibrations of the web’s silk lines
to tell what is going on around them. The spiders can
tell the difference between different sorts of vibrations and
where they are coming from in the web.
The
Orb Weaver’s web design provides a snare with a large catching
area that requires a minimum of silk and time to build. Slung
in spaces between shrubs or trees, they are very difficult for
flying insects to see and avoid. Thousands of sticky silk droplets
on the web’s spiral line glue struggling insects onto the
web, preventing their escape.
Orb
webs must be strong and elastic. Catching a fast flying insect
in an orb web is like snaring a jet fighter.
Spiders
only grip their webs with the middle claw and a few bristles
on the tips of their legs. Being on tippy-toes makes sure they
don’t get stuck. Spiders may also apply an ‘anti-stick’
substance when they groom their legs with their mouthparts.
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