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Bugged: Earth's insect population shrinks 27% in 30 years

Several recent reports have warned of a crushing decline in insect populations that could have a catastrophic effect on our environment and food supply.
Credit: AP
This undated photo provided by Michael Thomas in April 2020 shows a clouded sulphur butterfly in Cromwell, Conn. In an April 2020 interview, Ann Swengel, a citizen scientist tracking butterflies for more than 30 years, recalled that a few decades ago she would drive around Wisconsin “look out in a field and you’d see all these Sulphur butterflies around. I can’t think of the last time that I’ve seen that.” (Mike Thomas via AP)

Bumble bees are struggling. Fireflies are no longer lighting up the night, and fewer butterflies are fluttering over fields.

Several recent reports have warned of a crushing decline in insect populations that could have a catastrophic effect on our environment and food supply.

A big picture look at global insect decline shows land bugs are disappearing at a rate of nearly 1% a year. That means the world has lost more than a quarter of its insects in the last 30 years. 

Thursday's study in the journal Science finds the declines are more nuanced, varied and smaller than other studies. But scientists still call the results alarming and jaw dropping. 

Insects like bees are needed to pollinate much of our food. 

Scientists see no single global cause but fault habitat loss and urbanization. 

There's hope.

Freshwater bugs are increasing, likely due to cleaner rivers and streams.

"Insect populations are like logs of wood that are pushed under water. They want to come up, while we keep pushing them further down. But we can reduce the pressure so they can rise again," said Roel van Klink, a researcher at the German Centre for Integrative Biodiversity Research (iDiv) and Leipzig University.

"The freshwater insects have shown us this is possible. It's just not always easy to identify the causes of declines, and thus the most effective measures to reverse them. And these may also differ between locations."

'Critically understudied'

One of the first studies to signal the doom -- spurring reports of insect Armageddon -- came in 2017 when data from nature reserves in western Germany suggested that flying insects had declined by 75% over 27 years.

A review published in 2019 indicated that 40% of insect species could become extinct in the next few decades, with insect biomass projected to decline by a staggering 2.5% a year. That figure was quoted in other reports on the topic.

One of the reasons studying insect populations is so difficult is that there are more of them than any other type of animal on the planet -- there's said to be more ladybug species than mammals. So it's typically only the charismatic or commercially or medically important insects like butterflies, bees and mosquitoes that get studied.

What's more, because of their short life spans and population dynamics, insect populations are naturally highly variable, which presents a challenge for quantifying long-term trends, noted researchers Maria Dornelas of University of St. Andrews and Gergana Daskalova of the University of Edinburgh in commentary accompanying the study.

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"The phrase 'insect Armageddon' has captured the collective attention and shined a spotlight on one of the most numerous and diverse groups of organisms on the planet. Yet, insects are critically understudied," they wrote.

Even though it's the largest survey to date, this latest study's authors said the data they had used still had limitations. Existing research has focused on Europe and the United States, and the study had much less information on the outlook in Africa, South America and South Asia.

Data from protected areas and reserves was also more readily available, van Klink said. That means that locations where human land use is most intensive, and therefore where the strongest effects on insect trends might be expected, were underrepresented.

Given that the vast majority of insects are terrestrial, University of Sussex professor Dave Goulson said that this new study confirmed what was already clear -- that they have been declining for many decades.

"It isn't really at odds with the perception of widespread insect declines -- which is based almost entirely on studies of terrestrial insects (e.g. the German study), and which of course includes the pollinators; bees, butterflies, moths, hoverflies etc," Goulson, who authored a report describing insect declines as a quiet apocalypse, said via email.

"The contrasting trends for freshwater presumably reflects the big cleanup of water quality in recent decades, especially in Europe, and this is encouraging, as it suggests that it is possible to undo environmental damage. Unfortunately aquatic insects only make up about 10% of species, the rest being terrestrial," he added.

The figure "0.92% may not sound like much, but in fact it means 24% fewer insects in 30 years' time and 50% fewer over 75 years," van Klink said.

"Insect declines happen in a quiet way, and we don't take notice from one year to the next. It's like going back to the place where you grew up. It's only because you haven't been there for years that you suddenly realize how much has changed, and all too often not for the better."

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