Claudia Silva, of Corran School, asks :-

How does a spider know how to spin a web?

Simon Pollard, an arachnist (spider specialist) with the Canterbury Museum, responded.

Spiders have been around for about 380 million years and with an estimated 170,000 species, are an evolutionary success story with few rivals. The evolution of spider silk has certainly contributed to this success. Although all spiders make silk, about half spin silk webs to capture prey.

Web-building behaviour, like all behaviour, has evolved through the interaction of genetic and environmental factors. Spider genes for web-building behaviour are expressed in the development of the spider's nervous and hormonal systems, which in some ways can be compared to the 'hard-drive' on a computer. Some behaviours are very flexible and modified by experience, while others are more 'hard-wired' or innate. Web-building, is largely innate and learning from previous experience is not necessary for the spider to build a web. Young orb-web spiders can build a perfect web straight off.

Using external and internal cues, such as light levels, wind levels and hunger, the spiders' web-building' programme will 'run' and the spider builds a web in a pre-programmed sequence.