A pest is an animal which is detrimental to humans or human concerns.[1] It is a loosely defined term, often overlapping with the related terms vermin, weeds, parasites and pathogens. In its broadest sense, a pest is a competitor of humanity.[2]
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Often animals are derided as pests as they cause damage to agriculture by feeding on crops or parasitising livestock, such as codling moth on apples, or boll weevil on cotton. An animal could also be a pest when it causes damage to a wild ecosystem or carries germs within human habitats. Examples of these include those organisms which vector human disease, such as rats and fleas which carry the plague disease, mosquitoes which vector malaria, and ticks which carry Lyme disease.
The term pest may be used to refer specifically to harmful animals but is also often taken to mean all harmful organisms including weeds, plant pathogenic fungi and viruses. Pesticides are chemicals and other agents (e.g. beneficial micro-organisms) that are used to control or protect other organisms from pests. The related term vermin has much overlap with pest, but generally only includes those creatures that are seen to be vectors of diseases.
It is possible for an animal to be a pest in one setting but beneficial or domesticated in another (for example, European rabbits introduced to Australia caused ecological damage beyond the scale they inflicted in their natural habitat). Many weeds (plant pests) are also seen as useful under certain conditions, for instance Patterson's curse is often valued as food for honeybees and as a wildflower, even though it can poison livestock.
Plants may be consisidered pests if an invasive species. Any prolific animal or plant may be considered pests.
The greatest importance as pests (in the order of economic importance) are insects, mites, nematodes and gastropods.[3]
Some slugs are pests in both agriculture and gardens. Their significance is increasing drastically.[3] Deroceras reticulatum is a worldwide distributed slug pest.[3] Local importance slug pests include: Deroceras spp.,[3] Milax spp.,[3] Tandonia sp.,[3] Limax spp.,[3] Arion spp.[3] and some species of Veronicellidae:[3] Veronicella sloanei.[4]
Land snail pests include:
Freshwater snail pests include: