Answer: They're bloodsuckers.
This one seemed to be pretty easy - everyone who answered got it right: EricBess, Limited, Lythand, Melkor, mythosx, Oversoul, Ransac, rokapoke, sageridder, TomB, train, and turgy22
Scores:
EricBess: 10
Oversoul: 10
TomB: 10
train: 10
Melkor: 9
rokapoke: 9
sageridder: 9
DarthFerret: 8
Ransac: 8
turgy22: 8
Mooseman: 7
Lythand: 6
Limited: 5
mythosx: 3
cardboardbox: 0