Despite their small size, the sheer numbers or biomass of insects means that they have a significant impact on the environment and therefore upon our lives.
Although insects have never adapted to a truly marine environment, they inhabit almost all terrestrial and aquatic environments. Some have adapted to live with us (cockroaches, silverfish) while others live on us (lice, bed bugs, mosquitoes).
Their species richness or diversity surpasses any other group of organisms. It has been said that insects outnumber all the other species of animals and plants combined.
This relative diversity may be appreciated by a speciescape whereby the size of an organism, as drawn, is approximately proportional to the number of described species in the group (or taxon) that it represents.
We do not know how many species of insects there are. There are about 1 million named species. It has taken about 300 years for scientists to describe these. Estimates of actual species richness vary from less than 5 million to as many as 80 million. Figures at the higher end of these estimates are dependent upon the diversity of species now being recovered from the canopies of rainforests.
Obviously there are many years (if not centuries) of work for insect taxonomists to describe, name and classify these species.
Beetles are the largest group (or order) of insects. (The Mantophasmatodea is the smallest group with only a couple of recently discovered species in it.)
Both the number of insects and their diversity has led to the importance of insects in most aquatic and terrestrial food webs. They have roles as prey, predators, parasites and recyclers of dead matter, and many organisms, including most higher plants, could not exist without them.
There are many attributes of insects that have allowed for their success and diversification.
An insect may be of benefit to us or be regarded as a pest.
Most are beneficial or have an indirect influence.
Fewer than 0.1% are regarded as pests.
Plant pollination - Pollination by animals is more effective than by wind. Most higher plants are pollinated by animals, usually insects such as bees, wasps, flies and beetles.
Production of products - honey, bees wax and royal jelly (an export industry for Australia), silk (produced by the caterpillar, Bombyx mori), shellac (a varnish produced by a plant bug), cochineal (red food colouring produced by a plant bug) and 'Spanish fly' (a beetle and supposed aphrodisiac).
Nutrient recycling - by detritus and dung feeders and particularly in Australia by termites.
Human food - over 500 species of insects are used as food by humans -usually crickets, grasshoppers, beetle and moth larvae and termites. Australian aborigines regularly ate honeypot ants, adult bogong moths and the larvae of wood moths (witchety grubs). (see entomophagy).
Miscellaneous - Indigenous peoples (e.g. from PNG) often used butterflies and brightly coloured beetles as head or body decoration. Insect collecting is a common Western hobby and there is a small industry in arthropod pets.