The most characteristic feature of spiders is their ability to produce
silken threads. Spiders normally have six finger-like silk glands, called ‘spinnerets’ located beneath their abdomen. To spin a web,
the spider squeezes the silk out of its body through two small
holes. The liquid silk is thicker than water and dries into a fine
thread as soon as it comes in contact with air. Spider silk is much
stronger than steel and resists breakage because of its elasticity. It
can stretch up to 140 per cent of its original length. The diameter
of these silken threads is about 10,000 of an inch. Spiders use this
silk to make webs to trap their prey. The egg sacs of some spiders
are also made of silk which pretreats the unborn progeny. Sometimes the spider can also use its silk as a safety feature. A
certain species of spider ‘phidippus apacheanecs’ trails a safety
line of fine silk as it jumps. It uses the silk line to recover if it
misses its target. The silk of ‘Naphils Spider’ is the strongest
natural fibre known. The spinning of webs is a remarkable
example of instinctive behaviour. A spider does not have to learn
how to make a web, although spinning itself can be adopted to
unique circumstances. For example, ‘orb’ webs are circular in
shape and take an hour to build. Funnel spiders spin a net-like
entrance to their homes, which helps to trap food. Similarly, trap
door spiders dig their homes and spin a trap door out of their silk
for trapping insects. As integral components of our biosphere, spiders have an intrinsic existence value. They are efficient
predators that play an important role in controlling the pests of
cotton. They are also a source of food for other creatures, such as
birds and wasps. Thus, the presence of spiders is an ecological
indicator signaling the health of natural ecosystem. Questions: (1 x 5 = 5 Marks)
1. How does spider silk resists breakage?
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Spider silk is much stronger than steel and resists breakage because of its elasticity.
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