Pests
An organism that is seen as a threat to human beings or their interests is usually called a pest. Early man shared the natural resources with other organisms in its surroundings. In time people made ever-increasing demands on these resources. One result has been a great increase in the number of species that are now recognised as competitors of humans, usually referred to as pests. The definition of pest is, of course, very subjective. An ecologist would not necessarily think of a leaf-eating caterpillar on a plant as a pest, but a gardener who cultivates such a plant might very well do so.
A pest is an organism with characteristics that people see as damaging or unwanted, as it harms agriculture through feeding on crops or robbing the soil of nutrients intended for the crop. With the term pest, one naturally thinks of an animal or insect but it can equally refer to fungi or viruses. It is possible for an animal to be a pest in one setting but beneficial or domesticated in another. Likewise, many weeds can be extremely useful under certain conditions to encourage biodiversity. 
From the moment we started to cultivate land thousands of years ago to produce food for our family and community, we have had to contend with weeds, insects and diseases which are also in search of a good source of food.Not all these predators are bad and in fact biodiversity is essential to maintain a natural balance in the ecosystem. As part of good agricultural practice, farmers actively encourage biodiversity on their land.
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