The BBC offers a piece of fantastic footage of a Central American web-casting spider as it lowers the boom on an innocent and somewhat clueless cricket. You have to click through here to see it.

When the cricket touched one of the net’s anchoring threads with its antenna, it caused the spider to strike.
“It’s like a trip wire,” said Craig Walker, deputy team leader for invertebrates at the Zoological Society of London. “It’ll send a vibration to the spider.”
The spiders construct their webs in stages, first building a scaffold at a spot under which its prey is likely to pass.
“It’s almost like manufacturing your own workbench so that you can make something on it,” Mr Walker told BBC Nature.
The spider then carefully crafts its distinctive net using a different type of silk.
“They spin some of the silk at its most extended so its already at full stretch when its spun so that when its off the scaffold it’ll immediately shrink to its non-stretched size,” he said.
“They hit the prey with it at full stretch and then they relax it so that it gets caught into it, almost like a purse net.”

The speed and precision of it, the seeming forethought, the guile, are amazing and beautiful. Not so nice for the cricket, however.