Coevolution
A huge number of species are parasitic. A survey of the feeding habits of British insects showed that about 35% were parasites on plants, and slightly more were parasites on animals. That means that nearly 71% of insects in Britain are parasitic. Since British insects are better known than those elsewhere (because of the length of time they have been studied), this means that by far the majority of insect species throughout the world are parasitic. Another estimate went:p3