A pest is "a plant or animal detrimental to humans or human concerns (as agriculture or livestock production)"; alternative meanings include organisms that cause nuisance and epidemic disease associated with high mortality (specifically: plague). In its broadest sense, a pest is a competitor of humanity. In the past, the term might have been used for detrimental animals only, thus for example, causing confusion where the generic term 'pesticide' meant 'insecticide' to some people. It is any living organism which is invasive or prolific, detrimental, troublesome, noxious, destructive, a nuisance to either plants or animals, human or human concerns, livestock, human structures, wild ecosystems, etc. It is a loosely defined term, often overlapping with the related terms vermin, weed, plant and animal parasites and pathogens. It is possible for an organism to be a pest in one setting but beneficial, domesticated or acceptable in another.
Usage of the term 
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.
The term "plant pest" has a very specific definition in terms of the International Plant Protection Convention and phytosanitary measures worldwide. A pest is any species, strain or biotype of plant, animal, or pathogenic agent injurious to plants or plant products.
Plants may be considered pests if an invasive species. Any prolific animal or plant may be considered pests.
Invertebrate pests 
- Ants, cockroaches, flies and wasps are household pests, typically as they consume human food
- Aphids, larvass, grasshoppers and crickets cause damage to crop plants
- Lice, fleas and bed bugs can all cause skin irritation
- Mosquitoes, tsetse flies and kissing bugs cause irritation and carry disease
- Termites, silverfish, woodworm and wood ants cause structural damage
- Bookworms, carpet beetles and clothes moths cause non-structural damage
- Gypsy moths attack hardwood trees (see Gypsy moths in the United States)
- Chiggers cause skin irritation
- Sarcoptes scabiei causes scabies
- Ticks and mites cause irritation and can spread disease
Some slugs are pests in both agriculture and gardens. Their significance is increasing drastically. Deroceras reticulatum is a worldwide distributed slug pest. Local importance slug pests include: Deroceras spp., Milax spp., Tandonia sp., Limax spp., Arion spp. and some species of Veronicellidae: Veronicella sloanei.
Land snail pests include:
- Helix aspersa damages citrus fruits in California,
- Cernuella virgata, Theba pisana and Cochlicella spp. decrease quality of grains when harvested with the product in South Australia.
- Achatina fulica damages vegetables and ornamental plants in the Pacific region.
- Succinea costaricana damages ornamental plants in Costa Rica.
- Ovachlamys fulgens damages ornamental plants and orchids in Costa Rica.
- Other species considered to be pests include: Amphibulima patula dominicensis, Zachrysia provisoria and Bradybaena similaris.
Freshwater snail pests include:
- Pomacea canaliculata damages rice in Southeast Asia.
- Bulinus sp., Biomphalaria spp. and Oncomelania are intermediate hosts of schistosomes causing schistosomiasis.
- Various species in Lymnaeidae are intermediate hosts of fasciolosis.
Plant Pathogens 
Plant pests 
Vertebrate pests 
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- Mice, rats, and other small rodents cause infestations
- Foxes, opossums, raccoons, and bears eat waste
- Gophers, groundhogs, and moles destroy lawns
- Feral cats and feral dogs eat human food and carry disease
- White-tailed deer are now seen as pests in many suburban and exurban areas of the US, though not in more rural areas.
- Coyotes prey upon livestock
- Bats spread disease with their feces. also, fruit-eating bats eat stored human food.
- Eastern Grey Squirrels are seen as pests in Britain and Ireland because of the decline of Red Squirrel populations
- Wild boars damage crops, spread disease, and prey on livestock
- Pigeons and seagulls eat human food and carry disease[clarification needed]
- Many birds, such as crows, eat crop seed
- Canada Goose; non-migratory birds of this species are now widely regarded as pests in the United States (see Canada Goose#Relationship with humans).
- Woodpeckers peck at rooftops and also nest in them. They cause structural damage to homes (specifically houses).
See also 
- List of parasites of humans
- List of common household pests
- Invasive species
- Urban wildlife
- Pest control
- Nuisance wildlife management
- Home stored product entomology
- Miriam-Webster dictionary, accessed 22 August 2012.
- FAO Corporate Document Repository: Guidelines for Phytosanitary Certificates. Retrieved 2012-08-01.
- Speiser B. (2002). Chapter 219. Molluscicides. 506-508. doi:10.1201/NOE0824706326.ch219 PDF In: Pimentel D. (ed.) (2002). Encyclopedia of Pest Management. ISBN 978-0-8247-0632-6.
- Stange L. A. (created September 2004, updated March 2006). "Snails and Slugs of Regulatory Significance to Florida". Division of Plant Industry, Florida Department of Agriculture and Consumer Services. accessed 27 August 2010.
- Villalobos M. C., Monge-Nájera J., Barrientos Z. & Franco J. (1995). "Life cycle and field abundance of the snail Succinea costaricana (Stylommatophora: Succineidae), a tropical pest". Revista de Biología Tropical 43: 181-188. PDF.
- Barrientos Z. (1998). "Life history of the terrestrial snail Ovachlamys fulgens (Stylommatophora: Helicarionidae) under laboratory conditions". Revista de Biología Tropical 46(2): 369-384. PDF. HTM in the Google chache.
Further reading 
- Burch, John B.. 1960. Some snails and slugs of quarantine significance to the United States. U.S. Dept. Agriculture, Agricultural Research Service 82(1): 73 pp