The purpose of some insects

Even the nastiest insects have their place in the ecosystem. It is human internvention that causes problems. Agriculture on a big scale allows certain pests to thrive, so pest control is needed. Buildings provide warmth and food for other pests that would originally have survived in caves or warm spots.

Insects are also the natural food supply for other creatures. Some animal and bird species could become extinct if the insects they feed on were to be elmininated. Even plants die out when insects become rare. There is a type of orchid that relies solely on a certain type of butterfly, and those buttlerfly numbers have decreased due to other ecological reasons.