Pests are nonpathogenic organisms that compete with man for food or space, damage his possessions or attack him personally. The term "pest" is subjective: an ecologist would not necessarily consider several leaf-eating larvae as pests, but the gardener probably would. Generally, though, to be considered a pest, an animal, plant, or insect must occur in such abundance as to distinctly threaten man or his interests.
Most pests are invertebrate animals, especially insects, mites, nematodes, snails and slugs. Vertebrate pests include many kinds of rodents, birds and deer. Weeds are also usually considered pests.