In this 17-page PDF, Michael Hammes details six new swarm creatures. The oozling swarm, the wizard's doom, the lightning bug swarm -- all of these creatures are fully detailed with D20 System game statistics, origin and reproduction information, details on the swarms' diet and appearance, and where the swarm is most likely located (and under what circumstances a swarm is likely to be encountered).
Hyperlinked and bookmarked PDF. Very easy on your printer. Monster statistics are presented on single pages (except for the wizard's doom which is so large it requires two pages) so that DMs can print just the statistics they need.