Uses and Production
silk is incredibly tough and is stronger by weight than steel.
Quantitatively, spider silk is five times stronger than steel of the same
diameter. It has been suggested that a Boeing 747 could be stopped in
flight by a single pencil-width strand and spider silk is almost as strong as
Kevlar, the toughest man-made polymer. It is finer than the human hair
(most threads are a few microns in diameter) and is able to keep its strength
below -40°C. The toughest silk is the dragline silk from the Golden
Orb-Weaving spider (Nephilia clavipes), so-called
because it uses silk of a golden hue to make orb webs.
silk is also very elastic and capture silk (sticky silk for catching prey)
remains unbroken after being stretched 2-4 times its original length.
Spider silk is tougher, more elastic and more waterproof than silkworm silk so
it could have a much wider range of applications. It is simple to see why
spider silk is of such interest to materials chemists since new
ultra-strong fibres based on the silk could be developed.
use silk for a variety of functions:
silk for the wrapping and immobilisation of prey.
for catching prey using sticky silk – it is elastic to prevent the prey from
rebounding off the web.
which are used to connect the spider to the web, as safety lines in case a
spider should fall and as the non-sticky spokes of the web. Dragline
silk is the strongest kind of silk because it must support the weight of the
or ballooning which is used to aid the dispersal of young and to find
new areas as a food source. Silk is released and is caught by the wind
to lift the spider up into the air – flying spiders!
such as burrows or
male spiders weave sperm webs on which they deposit sperm and subsequently
transfer it to their front palps, ready for placing on a females genital
organs. Some species make a web and coat it with sex pheromones to
attract a mate.
are seven types of silk produced by seven silk glands. A single spider
does not possess all seven glands but has at least three if it is male
(dragline, attachment and swathing silk) or four if it is female. The
additional one is for egg sac silk. The seven types of gland are:
gland: swathing silk.
gland: egg sac silk.
glands (major and minor): non-sticky dragline silk. Silk from the
minor ampullate gland is only half as strong as that from the major gland.
gland: attaching threads – attachment discs are made which anchor a
thread to a surface or another thread.
gland: core fibres of sticky silk.
gland: outer part of sticky silk – droplets of an adhesive substance are
deposited along the threads.
of Tina Carvlho, Microangela
glands are located on the lower side of the abdomen (see diagram below) and
contain a watery fluid known as ‘dope’. This fluid passes through to the
spinneret via a multitude of microscopic tubes where water recovery and
solidification begins. Fluid from different glands can lead to the same
spinneret so silk with specific properties required for a particular function
can be produced. There are usually three pairs of spinnerets but this can
vary between 1 and 4 pairs depending on the species. The substance exits
through the spiggots which are mobile, finger-like protrusions and the resulting
silk emerges as a solid. There are many spigots so many fibres are bound
together like a cable. The diameter of a single fibre is controlled by the
muscular action of a valve. The faster and tighter the strand is drawn,
the stronger the silk.
Picture from reference 11
interesting web facts:
all spiders weave webs.
do not stick to their own web because only the central spiral part of the
web is sticky, not the spokes. The spider knows where to tread!
lose their stickiness after about a day due to factors such as dust
accumulation and exposure to air. In order to save energy the spider
eats its own web before making a new one so the protein used for the silk
threads is recycled.