A Visual Guide to these Eight-Legged Wonders.
 
Spiders are in the arachnid class, but not all arachnids are spiders.  Most spiders use a web to catch their prey, which comes from spinneret glands on their abdomen, and each gland produces a different kind of silk - some sticky, some fine, and some for building.
 
This Discover Spiders book provides a valuable introduction to these creatures and their world.