12 December 2019
Are we witnessing an insect apocalypse? It is complicated. The longest running study of insect populations in the world shows that the total mass of moths in Great Britain is double what it was in the 1960s, but has been declining by around 10 per cent a decade since the 1980s. This probably reflects what has happened to other kinds of insects, too.
“Is this a good news story? No it’s not, because we still have this long-term decline,” says Callum Macgregor at the University of York in the UK, who on 11 December gave a talk on the findings at a meeting of the British Ecological Society in Belfast.
His team analysed data from 34 sites in Wales, Scotland and England where insects have been trapped nightly starting as early as 1967, as part of the Rothamsted Insect Survey. The results show there are big variations in moth biomass from year to year and from species to species, but overall biomass rose sharply from the 1960s to the 1980s and then began declining gradually.
Because the moth biomass trends in later years match those seen in studies of other types of insects, Macgregor thinks the overall biomass of all insects in Great Britain is probably twice as high today as it was in the 1960s.
In the past two years, there has been much talk about a global “insect apocalypse” or “insectageddon”. This idea stems from a 2017 study that found a steep decline in insect biomass in Germany since 1989.
However, many ecologists have cautioned that there are too few studies around the world going back far enough in time to justify such a sweeping conclusion. It is likely that many insect populations in many parts of the world, especially in the tropics, are declining because of habitat loss and climate change, but we just don’t know.
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“The severe population collapses being claimed by the insect apocalypse narrative are not supported by the most comprehensive long-term insect monitoring programme in the world, the Rothamsted Insect Survey,” Manu Saunders at the University of New England in Australia wrote in a commentary on the study.
“We should be concerned,” says Stephen Heard at the University of New Brunswick in Canada. “But, for me, the insect armageddon thing is too much over the top.”
Macgregor says the findings do match what has been seen in Germany from the 1980s onwards – it is what happened before then where the picture looks very different.
The findings don’t provide any clear answer. The biggest declines since the 1980s have been in woodland and grassland locations, rather than sites on farms or in urban areas, says Macgregor.
Journal reference: Nature Ecology & Evolution, DOI: 10.1038/s41559-019-1028-6
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