Their experiments have shown that common house spiders spin their webs in different ways according to the psychotropic drug they have been given. Spiders on marijuana made a reasonable stab at spinning webs but appeared to lose concentration about half-way through. Those on Benzedrine - "speed" - spin their webs "with great gusto, but apparently without much planning leaving large holes", according to New Scientist magazine.

Caffeine, one of the most common drugs consumed by Britons in soft drinks, tea and coffee, makes spiders incapable of spinning anything better than a few threads strung together at random. On chloral hydrat, an ingredient of sleeping pills, spiders "drop off before they even get started".

Nasa scientists believe the research demonstrates that web-spinning spiders can be used to test drugs because the more toxic the chemical, the more deformed was the web.

The scientists believe their previous work on the goemetry of crystals will help them to devise computer programs that can analyse web-building objectively in order to predict the toxicity of new medicines. "It appears that one of the most telling measures of toxicity is a decrease, in comparison with a normal web, of the numbers of completed sides [of a web]; the greater the toxicity, the more sides the spider fails to complete", the scientists say.

Paul Hillard, spider specialist at the Natural History Museum in London, said researchers first discovered the effects of psychotropic drugs on spiders during experiments at the end of 1960s. The researchers fed caffeine to spiders in hope of making them spin webs in the late evening rather than the early dawn. The result was eccentric webs rather than earlier spinning, he said.