Opinions are divided about insects. For some of us, insects are beautiful, fascinating, joyful creatures – their buzz or fluttering by a vital part of our spring and summer. Ecologists, farmers and gardeners might value for them for the good they do, pollinating flowers, recycling nutrients, controlling unwanted garden visitors, providing food for birds and so on
On the other hand, sadly, there are many for whom the idea of fewer insects seems attractive, for insects are often associated with annoyance, bites, stings and the spread of disease. When recently asked about the seriousness of global wildlife declines on national UK radio, medical doctor, professor and well-known TV presenter Lord Robert Winston replied: “There are quite a lot of insects we don’t really need on the planet”. This response likely epitomises the attitude of many.
Insects make up the bulk of known species and are intimately involved in all terrestrial and freshwater food webs. Without insects, a multitude of birds, bats, reptiles, amphibians, small mammals and fish would disappear, for they would have nothing to eat. 87% of all plant species require animal pollination, most of it delivered by insects [Ollerton et al. 2011]. That is pretty much all of them aside from the grasses and conifers. Approximately three-quarters of all crop types grown by humans require pollination by insects, a service estimated to be worth between $235 billion and $577 billion per year worldwide [Lautenbach et al. 2012]. Financial aspects aside, we could not feed the global human population without pollinators.
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.