Kōrero: Spiders and other arachnids

Whārangi 2. Webs

Ngā whakaahua

Why do spiders produce webs?

We usually see spiderwebs more often than we see spiders. About half of all spiders build webs to catch prey, while the others use stealth, speed and ambush, and are commonly called hunting spiders.

Spiderwebs effectively increase the size of the spider and provide it with information that would normally be outside the range of its senses. A spider’s web extends the range over which the vibrations of a moving insect can be felt.

Web spiders use their feet to ‘listen’ for the vibrations that signal that their prey has touched the silken lines of the web. They then run across to the prey and immobilise it with venom. They add glue droplets to silk or entangling threads, so that prey stick to the web.

Producing silk

At the end of their abdomen, spiders have tiny tubes called spinnerets, used for producing silk. In the abdomen are silk-making glands, inside which the silk is a liquid protein. The spider squeezes silk from these glands and into the spinnerets. It uses hairs on its fourth pair of legs to pull the liquid silk through the spinnerets. The tension of this movement makes the protein molecules line up, and the silk solidifies into a thread.

Spiders use silk in different ways throughout their lives – to trap and wrap up prey, as a safety line if they fall, to build nests, and to protect their eggs.

Spider silk is the strongest natural fibre known. One strand is about five times stronger than a strand of steel of the same width. Silk is also very elastic and can be stretched to 130% of its original length.

Why don’t spiders get caught in a web?

Many spiders have a coating of oil on their feet, which stops them from getting glued down. Most also tread carefully, to ensure that they don’t get tangled. But sometimes an unfortunate spider can get caught in a web.

Me pēnei te tohu i te whārangi:

Simon Pollard, 'Spiders and other arachnids - Webs', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/spiders-and-other-arachnids/page-2 (accessed 23 November 2017)

Story by Simon Pollard, published 24 Sep 2007