By Jane Hughes
By Jane Hughes
28 November 1999
Scientists have discovered that the "modern" spider has been in existence for longer than the dinosaurs.
Two finds of fossil spiders in excavations of prehistoric lakes in South Africa and Virginia, in the United States, have revealed that the modern spider was walking the earth 240 million years ago, making it three times older than previously thought.
The modern spider split from its primitive counterpart - which resembled the present-day tarantula and funnelweb spiders - in an adaptive move to catch the increasing number of airborne insects.
It shrank to an average size of one inch or smaller and its large hairy legs gradually became more slender.
As the modern spider got smaller it began to use its web as a sensory field in the air, replacing the underground strands used by primitive relations, which lived mainly in burrows.
The poisonous claws used by tarantulas and their ilk for stabbing prey as they chased it along the ground or trapped it against a tree trunk evolved into pincer-like grips, twisted together in front of the spider so that it could lift insects out of its web.
"The spider is the most abundant predator on land because it has such a large food source but it is very rare to find it in fossilised form, particularly in such a complete state," said Dr Paul Selden, a senior lecturer in palaeontology at Manchester University, who has written a paper on the fossils.
"Spiders were nimble walkers and were pretty good at not falling in water, so for every spider fossil there will be thousands of insect ones."
Spiders had evolved sufficiently to survive the catastrophic events of about 65 million years ago, when it is believed that the impact of a massive comet shrouded the earth in smog, killing off the dinosaurs and many other species.
However the spiders continued to evolve to improve their hunting and evasion techniques and today the biggest family of spiders is the jumping variety.
"The jumping spiders have got rid of webs and use their silk to make little sleeping bags instead but they spend much of the day wandering around looking for insects to jump on," said Dr Seldon.
"The trouble with a web is that it advertises the spider's presence and means they are relatively static, whereas jumping makes it easier to catch prey and escape from predators."