vermin

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun plural Various small animals, such as rats or cockroaches, that are destructive, annoying, or injurious to health.
• noun plural Animals that prey on farm animals or game or that destroy crops.
• noun plural People considered loathsome or repulsive.

from The Century Dictionary.

• To rid or clear of vermin.
• noun Any noxious or troublesome animal: mostly used in a collective sense.
• noun A worm; a reptile.
• noun A noxious or disgusting insect, especially a parasite; particularly, a louse, a bedbug, or a flea, A mammal or bird injurious to game, aud mischievous or troublesome in game-preserves: chiefly an English usage. Such quadrupeds as badgers, otters, weasels, polecats, rats, and mice, and such birds as hawks and owls, are all called vermin.
• noun Hence A contemptible or obnoxious person; a low or vile fellow; also, such persons collectively.

from the GNU version of the Collaborative International Dictionary of English.

• noun obsolete An animal, in general.
• noun A noxious or mischievous animal; especially, noxious little animals or insects, collectively, as squirrels, rats, mice, worms, flies, lice, bugs, etc.
• noun Hence, in contempt, noxious human beings.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable or uncountable Animals that prey on game, such as foxes or weasels.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various small animals or insects that are pests; e.g. cockroaches or rats
• noun an irritating or obnoxious person