Locust swarms will intensify with climate change, threatening food security, study finds

There's a good reason locusts are considered plague-worthy. Despite their size, swarms of these insects can cause considerable damage by shredding plant life to bits like ravenous piranhas.. The bugs destroyed millions of American lives during the so-called "Dust Bowl" of the 1930s and caused massive hardship in East Africa from 2019 to 2020 — perhaps the authors of the Exodus were right to vilify the notoriously gluttonous insects.

Despite the human tendency to demonize these bugs, they are a natural part of the world and can serve important ecological functions while at the same time being extremely destructive. Nonetheless, locusts pose big risks to human agriculture and food security, as laid bare by a recent study from the journal Science Advances. It details that, as climate change worsens, locusts will expand their ranges in the very same North African and Middle Eastern regions where the Bible is set.

It all comes down to the weather. As humans continue to burn fossil fuels and thereby release greenhouse gases into the atmosphere, Earth's temperature will continue to warm. Researchers from China and Singapore found that this will increase the prevalence of cyclical droughts and heavy rains in North Africa and the Middle East — and those are ideal conditions for locust swarms. Their eggs will thrive in the damp soil, and as vegetation grows sparse, they will congregate into groups with billions of individuals seeking food while flying up to 90 miles every day.

The United Nations has already described locusts as “the most destructive migratory pest in the world," and that will have been the case before climate change encourages even more swarming behavior. According to the authors of the Science Advances paper, their model finds that locusts' range could expand by as much as 13 to 25 percent because of global warming, imperiling food security all over the world.

"A warming climate will lead to widespread increases in locust outbreaks with emerging hotspots in west central Asia, posing additional challenges to the global coordination of locust control," the authors write, noting that locust populations have always relied on climate conditions, thriving or declining from dryness, precipitation and flood frequency to wind speed, air temperature and soil moisture. Everything from how locusts breed and incubate to their migration patterns is shaped by climate and weather conditions. As a result, weather events like the El Niño–Southern Oscillation are crucial in determining whether locusts are abundant or comparatively scarce.

"We find a strong teleconnection between the recurring climate variation and locust dynamics," the authors write. "The transition between the positive (El Niño) and negative (La Niña) phases of [the El Niño–Southern Oscillation] affects the abundance and distribution of locusts. Highly active areas contributing to locust dynamics are 65% larger during El Niño years than La Niña years."

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Cyril Piou, an ecologist at France's Center for Biology and Management of Populations, criticized the study to Inside Climate News by arguing that it did not sufficiently collaborate with scientists from that region. Had they done so, Piou argued, they might have taken local conditions like pest control programs into consideration.

“There are many scientists in these countries that actually know a lot about locust ecology and management,” Piou told Inside Climate News. “And [the researchers] could have gotten some grasp of this information to avoid arriving at conclusions… without knowing what’s happening already on the ground.”

Other recent research has indicated the ways in which climate change is helping insect populations that humans wish to see hindered. A December study from the Journal of Agricultural and Food Research found that agricultural insect pests will thrive as climate change worsens. Elevated carbon dioxide concentrations, worsening droughts and higher temperatures will all reduce crop production while working to the advantage of a number of insect pest species.

"Global warming could increase insect populations, resulting in earlier infestations and crop damage," the authors explain. "Optimal temperatures for many insect pests could increase pest infestations under global warming scenarios. However, a uniform increase in pest abundance and crop losses is not guaranteed due to varying needs, tolerances, and temperature effects among insects."

This finding is similar to that from a 2021 article in the journal Insects. The authors of that piece also found that climate change will be a boon to certain types of agricultural insect pests.

"Changes in climate can affect insect pests in several ways," the authors explained. "They can result in an expansion of their geographic distribution, increased survival during overwintering, increased number of generations, altered synchrony between plants and pests, altered interspecific interaction, increased risk of invasion by migratory pests, increased incidence of insect-transmitted plant diseases, and reduced effectiveness of biological control, especially natural enemies."

It is important to note that both of those studies did not claim climate change would be a blanket benefit to insect pests; because species are so different from each other, it is possible that certain ones will falter instead. This point was also made in a 2020 study for the journal Frontiers in Ecology and the Environment, which similarly examined how global insect pests will react to climate change. After analyzing 31 plant-eating insect pest species, they found that for a majority the severity of their threat to humanity was impacted (for better or worse) by climate change.

"Among these insect species, 41% showed responses expected to lead to increased pest damage, whereas only 4% exhibited responses consistent with reduced effects; notably, most of these species (55%) demonstrated mixed responses," the authors concluded. "This means that the severity of a given insect pest may both increase and decrease with ongoing climate warming."

If one thing is certain, it is that as the Earth continues to overheat, the types of weather conditions that benefit pests and disadvantage crops will become more and more common. As a study last year in the journal PNAS demonstrated, climate change if left unchecked will eventually lead to so-called compound drought and heatwaves (or CDHW events), which will happen roughly twice a year with each one lasting approximately 25 days. This is bad news for humans, but great news for pests like locusts. If our species wishes to avoid this outcome, it must prevent a warmed Earth from becoming a new normal.