As you know if you've read Spider Silk, spiders' most voracious predators are wasps. Over at Jerry Coyne's Why Evolution Is True blog, Matthew Cobb has an illuminating post about potter wasps. Potter wasps don't prey on spiders; they prefer caterpillars. But like araneophagic wasps, they guarantee their young get their meals in an ultra-fresh state: mother wasps sting and paralyze caterpillars and stock them live in the nests where they lay their eggs. The growing wasp larvae chew through prey that's not yet perished.
The core of Cobb's post is his explanation, based on a 1978 paper by Andrew P. Smith, of the decision-making process the wasp goes through as it builds the fortress and feeding chamber for its offspring. Experiments and observations of the type Cobb outlines give us tremendous insight into many of the behaviors of minute organisms--including spiders--that at first seem inexplicably complex.
Cobb first wrote this post for Pestival, the insect arts festival, which I hope is coming to a venue near you soon.