A pest is any organism harmful to humans or human concerns. The term is particularly used for creatures that damage crops, livestock, and forestry or cause a nuisance to people, especially in their homes. Humans have modified the environment for their own purposes and are intolerant of other creatures occupying the same space when their activities impact adversely on human objectives. Thus, an elephant is unobjectionable in its natural habitat but a pest when it tramples crops.
Some animals are disliked because they bite or sting; wolves, snakes, wasps, ants, bees, bed bugs, mosquitos, fleas and ticks belong in this category. Others enter the home; these include houseflies, which land on and contaminate food; beetles, which tunnel into the woodwork; and other animals that scuttle about on the floor at night, like rats, mice, and cockroaches, which are often associated with unsanitary conditions.
