On pests in general

One might get the impression that all the world’s invertebrate animals are wholly bent on making life difficult for us, but in fact only a tiny proportion of them can be regarded as pests.

The insects are, of course, by far the largest group in the animal kingdom, and they also include the largest number of pests. It is estimated that about a million different insect species have been described, but far fewer than one in a thousand of these can be accused of causing damage or injury of one kind or another to man. And of course some insects are beneficial to man.

It is difficult to define exactly what an animal pest is. There are certain species which are exclusively adapted for plaguing us and the body louse is a good example, but there are not many to which the term pest can reasonably be applied. It may be sufficient to say that some species under certain conditions may become as numerous as to encroach on some of man’s interests, and must therefore be regarded as pests. This does not preclude the possibility that under different conditions they may be harmless, or possibly even beneficial.

In modern agriculture and forestry the aim of pest control is normally not to exterminate the pest animals concerned. In the majority of cases it will be a much sounder principle to reduce them to a level where the damage they cause can be tolerated, the actual level depending upon economic considerations.

It is rather more difficult to decide how many invertebrates can be tolerated in a home. Most people will not be concerned if there are a few flies buzzing around the lights or the odd spider in a corner of the garden shed, but it must be recognized that for some people the presence of a single invertebrate in the house is a traumatic experience.