The importance of insects is often justified in terms of ecosystem services (in simple terms, the benefits they provide to humans), which can be ascribed a monetary value. In addition to pollination, insects such as ladybirds, hoverflies, ground beetles and lacewings are important biocontrol agents (often controlling other insect numbers). Woodboring beetles and wasps help to recycle the nutrients in decaying timber, while an army of tiny invertebrates including springtails, silverfish, worms and woodlice help to break down the leaves that fall every autumn. Animal dung would build up in our pastures were it not for the prompt arrival of dung beetles and flies, which swiftly recycle it, providing nutrients for the grass to grow. Animal corpses, which otherwise might take months to rot, are rapidly consumed by maggots and carrion beetles. Ants and other burrowing insects help to aerate the soil and disperse seeds. Silk moths give us silk and honeybees provide us with honey [reviewed in Noriega et al. 2018]. These ecosystem services are estimated to be worth at least $57 billion per year in the United States alone [Losey and Vaughan 2006].

For many insects, we simply do not know what they do. We have not even given a name to perhaps four-fifths of the estimated five million insect species that are thought to exist, let alone studied what ecological roles they might perform. As Aldo Leopold said: “The first rule of intelligent tinkering is to keep all the parts”. We are nowhere near understanding the multitude of interactions that occur between the thousands of organisms that comprise most ecological communities, and so cannot say which insects we ‘need’ and which ones we do not. Studies of crop pollination have found that most tends to be done by a small number of species, but that pollination is more reliable and resilient when more species are present.

Excerpt from:  Insect Declines and Why they Matter Professor Dave Goulson, FRES.