Human impacts on the environment are so widespread and have increased so rapidly that they are together referred to as global change: a cocktail of pressures including land-use and climate change, pollution, the spread of non-native species, and the over-exploitation of natural resources. As humanity transforms the global environment, research into the responses of insects can offer valuable insights to help us protect cherished wildlife and the ecosystems on which we depend.
Insects flutter, crawl and scurry throughout the world’s ecosystems, fulfilling myriad roles from pollination to pest control to the recycling of carrion and dung. Short life cycles mean that insect numbers rise and fall dramatically in response to changes in the physical environment and in the plants, microbes and animals with which they interact. Insects are ubiquitous, sensitive and versatile indicators of change, and a flurry of recent reports of their demise has prompted alarm about the wider significance for nature and human life.
The real picture is more complicated but no less worthy of urgent investigation. Whilst some well-studied insects including bees and butterflies are known to have declined as much as better known animals like vertebrates, we simply do not have enough evidence about trends in the abundance and distribution of most insects in most parts of the world. But we can gain pointers about the likely fate of insects, and what to do about it, by combining scientific theory and experiments with innovative analyses of information from a wide range of sources.
The pressures that insects are facing depend on where they live. In traditionally damp and cool places like the British Isles, hotter summers have allowed insects including many moths and dragonflies to colonise locations further north. Meanwhile, in sunny Spain, increasing heat and drought are confining some dung beetles and butterflies (such as the Apollo) to the coolest mountaintops. Often, insects that are struggling with habitat loss because of urbanisation or intensive agriculture are also faced with challenges from pollution and climate change. These combined pressures can prevent adaptation to each individual threat, and habitat loss has stopped insects from colonising as far north in Europe and North America as would be expected from rates of climate warming alone. Even where intact habitats remain, such as tropical forest enclaves in Central America, the numbers and distributions of moth caterpillars suggest that insects are feeling the heat from climate change.
We are now beginning to piece together a more reliable and informative picture of how insects are responding to global change thanks to records collected by scientists and volunteers for half a century or more. The gold standard of evidence comes from programmes using systematic monitoring such as the UK Butterfly Monitoring Scheme, which since the 1970s has acted as a template for insect monitoring more widely. Researchers are also increasingly detecting the status and trends of insects by making use of records from historical museum collections and citizen science. In some cases, these sources indicate the remedies for insects to recover from declines: since the implementation of clean water regulation in the 1990s, freshwater groups like mayflies and caddisflies that inhabit rivers and ponds have shown clear signs of recovery.
We still face important challenges in diagnosing the threats posed to insects by global change and in administering the cures. We lack information about how tropical insects, the most diverse animals in the world, are responding to deforestation and climate change: and the news is unlikely to be good. As much as possible, we need to protect and manage natural habitats both for biodiversity and for their roles in regulating the climate; and we need innovative and inclusive schemes to monitor insects and their responses both to global change and to conservation efforts. Combining this set of approaches will equip us with strong evidence on which to base conservation measures, and a functioning set of ecosystems to help support a human population that is engaged with the insects with which we share our world.
Rob Wilson
Museo Nacional de Ciencias Naturales (Madrid, Spain) and BC member since 1988.
This blog is based on a scientific paper Insect responses to global change offer signposts for biodiversity and conservation published recently by Rob and Butterfly Conservation’s Richard Fox in the journal Ecological Entomology. The full text can be read here.