In the 1950’s Dr. Peter Witt gave spiders various chemicals to see the effect on their webs. He tried 23 substances including: caffeine, carbon dioxide, carbon monoxide, strychnine, histamine, mescaline, and LSD. The results are documented in his book, Spider Communication. Some of his pictures are at Cannibis.net.
In 1995, David Noever at NASA repeated the experiment with these results:
The marijuana spider did pretty good, but stopped about halfway through. The benzedrine (amphetamine) spider worked hard, but failed to do much planning. The caffeine spider was just ineffective, and the chloral hydrate (sedative) spider fell asleep.
This short film sums it up. It starts out slow, but make sure you watch it all the way through.