Insects, the most abundant and diverse animals on Earth, are facing a crisis of epic proportions, according to a growing body of research and a rash of alarmist media reports that have followed. If left unchecked, some scientists say, recent population declines could one day lead to a world without insects.
“The Insect Apocalypse Is Here,” New York Times Magazine avowed in an in-depth story examining the trend, while other outlets have warned of animpending “ecological Armageddon” for life on Earth if insects keep vanishing. The resulting void, they say, would ripple out to affect every level of the food chain — even the nitrogen cycle for plants.
Most alarmingly, a review published in Biological Conservation highlighted “dreadful” circumstances for insects, with about 50 percent experiencing a decrease in numbers and a third threatened with extinction. The scientists analyzed 73 studies of insect declines and concluded that if nothing changes, all insects will be wiped out by the end of the century.
The frightening claim rests largely on three of the longest studies. Most notable was a 2017 German survey of flying insects by amateur entomologists, which saw a 76 percent decline in biomass in less than three decades. According to another study, from 1970 to 1999 three-fourths of British butterflies saw their populations drop while an analysis of ground-dwelling arthropods in the Puerto Rican rainforest found populations have fallen 10 to 60 times compared to levels seen in 1976, which was correlated with a decline in frogs, reptiles, and birds.
“We don’t think it’s alarmist to say that it’s a catastrophic event. It iscatastrophic,” review author Francisco Sánchez-Bayo says in a video call, explaining why his paper strikes a more alarmist tone than previous studies. “We are alerting people that we have here a serious problem and we have to solve it.”
Nonetheless, the research and reporting that followed may not accurately characterize the current and future state of insects.
“I’ve got a sort of mix of feelings because obviously it’s really nice to see that people are actually concerned about insect declines and recognize this is a very serious issue,” says Gavin Broad, a self-described “wasp botherer” and principal curator of the insect collection at the Natural History Museum in London.
But he and others question if panic is appropriate, saying what this data chiefly represents is how little we know about the insect world. We’re so ignorant about bugs that when researchers recently extracted and analyzed DNA from the soil of the small forested island of Hauturua, New Zealand, they may have found up to 2500 new species. There’s just too little known about insect numbers to draw conclusions about where they’re headed right now. But the declines are worrying nonetheless.
A World Without Insects?
If living creatures were organized in a pyramid, insects would largely make up the base. With an estimated seven million different species, arthropods outweigh humans by about 17 times, although 80 percent of those are likely still undiscovered. Their sheer numbers and ubiquity across the planet mean that drops in insect populations are a big deal, even if they don’t disappear completely. Birds, mammals and other creatures with bug-based diets might starve, and flowering plants that rely on pollinators could lose their ability to reproduce.
However, some of the more alarming conclusions may rest on shaky data. For example, the insect extinction predicted by the Biological Conservationreview study is not at all likely, according to experts. That conclusion is based on extrapolations from studies that looked only at specific insects in certain locations.
For example, the German study assessed insect traps at 96 different sites at different times between 1989 and 2016. More than half of the locations were only sampled once. The so-called malaise traps they used are tent-like structures that funnel buzzing bugs into a tube filled with ethanol. This gooey graveyard is then weighed, accounting for the fluid. But it only snares flying insects, ignoring bugs that swim or walk. The data from studies like this is fundamental to insect research, but not nearly enough to make sweeping claims.
A cicada. The insects can remain underground for over a decade before emerging to reproduce. (Credit: SIMON SHIM/Shutterstock)
“You can’t just draw a line through some data points, take it down to zero and say, ‘Right, that’s how long we’ve got,’” Broad says. “That’s not how stats works, it’s not how insect populations work, either.”
Indeed, insect populations can fluctuate wildly: take cicadas and their lengthy underground gestation periods. In Puerto Rico, biomass was only collected six times: twice in the 1970’s, and four times between 2011 and 2013. The data revealed a statistically significant drop in average biomass, but it represents just a few snapshots of a complex environment. Broad says it’s difficult to look at samples taken four decades apart and pick out a distinct trend.
Most of the studies also rely heavily on measuring biomass, meaning that they calculate the weight of bugs caught in traps. While these measurements do reveal a sharp decline, according to Broad, they don’t include the number of species collected, so a few large-bodied species could disproportionately distort results. In other words, you can’t tell how many different types of insects there are based on weight alone.
Sánchez-Bayo and his co-author Kris Wyckhuys have also been criticized for only including studies with the keyword “decline,” in their review, which could mean that they missed studies of insects who aren’t in trouble. The result might be data that looks unfairly gloomy, and it casts doubt on whether insects are truly in as much trouble as they claim.
In Defense
Sánchez-Bayo, a biologist at the University of Sydney, acknowledges the shortcomings of his work, but he says he’s only interpreting the data available. “If someone wants to criticize that, please show us your own studies, show us your measurements, and show us that it’s different,” he says, adding that extinction wasn’t the main point of his research. “This is just an extrapolation and we don’t put too much emphasis on that.”
Furthermore, he says that two-thirds of the studies came from references in papers he found outside the database search, though they weren’t able to include that methodological detail in their paper because of length constraints. Sánchez-Bayo says it contradicts the criticism that the authors only looked for papers mentioning insect declines. And a decline in biomass could still predicate ecosystem collapse, he argues, because the larger animals are always the first to go, so even if heavy bugs are dying off disproportionately, it could presage a larger event.
But, methodological disagreements aside, the data in aggregate suggests serious issues for insects, even if the data looks a bit patchy up close. Habitat change, pollution, and intensive agricultural practices are clearly killing insects, with implications for the rest of us. We need to act before it’s too late, Sánchez-Bayo insists.
The Unknown Universe of Bugs That we need more data on insects, especially the kind of long-term studies Sánchez-Bayo found wanting, is something most researchers agree on. More information would help scientists tell the difference between worrying declines and wholesale extinction.
“There is an urgent need for more data, particularly longitudinal studies,” said Robert Peterson, president of the Entomological Society of America in a recent statement.
It’s not enough to just survey insect populations — it needs to be done thoroughly, over many years, explains Kaitlin Whitney, an insect ecologist and assistant professor at the Rochester Institute of Technology. The amount of time for which a study gathers data plays a significant role in the results, she says, and while most of these studies included datasets covering more than 10 years, that isn’t true for all of them.
“The majority of really any kind of environmental science and ecology data happens in two or three years chunks. It’s often the length of somebody’s dissertation,” Whitney says. She and her colleagues are in the process of analyzing 17,000 long-term environmental datasets to learn how short-term data can be misleading. “If you only take a two or three year snapshot, you end up missing a broader population trend. So long-term data is really tricky to get, but there’s a lot of noise in short-term data.”
Problems arise when scientists try to draw broad conclusions from data that’s too sparse or too narrow, she says. For example, Whitney points to a 2015 study in the Journal of Insect Conservation in which 117,000 dead insects were collected along a 2-kilometer stretch of highway in Ontario. The authors then used this data to estimate that “hundreds of billions” of insects are killed at roads across North America.
“We just have no idea if that’s true,” Whitney says. “There’s no reason to believe that declines or even road mortality from one highway stretch in Canada is indicative of what’s happening across the rest of the continent … We just don’t have global surveillance of insects to be able to make a reasonable estimate like that.”
But such is the quality of data that insect researchers must work with when assessing the health of insect populations. More research would help, but it’s extremely difficult to get funding for longer-term insect inventories, Whitney says.
Funding challenges and workplace shortages have plagued entomology departments in recent years, while most modern biology textbookscompletely gloss over bugs and spiders. In addition, insect research has focused disproportionately on industrial pollinators, such as honeybees, which are technically domesticated, leaving a shortage of data on wild species.
“It’s not surprising that that study in Germany that’s started getting a lot of this press on insect declines was from a group of hobbyists,” Whitney says.
Even the insects we do know about often aren’t well understood. The London National History Museum, for example, houses some 34 million specimens dating as far back as 1650. However, Broad says, “A huge number of species of insects we have in our collections here, we don’t know anything about them, other than a name and as a specimen or two in the collection.”
Ignorance As A Motivator
None of this is to say that insects don’t need environmental protections, of course — only that we’re not really aware of how severe the problem is yet, which makes it difficult to devise conservation strategies. After all, according to the World Wildlife Foundation’s most recent report, wildlife population sizes have shrunk by 60 percent since 1970, so it seems likely insects have declined as well.
A species need not even go extinct for its absence to be felt. Animals are said to be “functionally extinct” when population levels fall so low that they can no longer fulfill their traditional role in an ecosystem. This happened with dung beetles in the Amazon, whose numbers declined so far that the dung they normally disposed of began to build up, spreading parasites like nematodes. Seeds that they normally dispersed were instead eaten by rodents, and animals that fed on the beetles were left without a common source of food. Even without disappearing, the dung beetles’ caused ecological tremors, and the same could go for other species of insect.
(Credit: Neil Bromhall/Shutterstock)
“I’m not sure that we don’t have anything to worry about, but I’m also not sure that we should be panicking,” Whitney maintains, adding that if we truly want to help, we need to better understand the complex ecological roles insects play in different environments around the world.
We’re starting to see more of that. Last month, Svenja Schulze, the German Federal Minister for Environment, proposed €100 million ($113 million) for an insect protection law that would curtail the use of fertilizers and pesticides. It reserves €25 million for research. The money could begin revealing the complex ways that insects interact with their environments, which can be key to protecting them. And the fact that we don’t know enough about how threatened they truly are shouldn’t encourage people to stop caring about conservation. At the end of the day, it’s our responsibility to lessen our impact on our environment, Broad says.
“We have a moral obligation to try and help because we have trashed everything so much,” Broad says. “Every potential extinction is just really sad. 770 million years of evolution, just gone like that, often for very silly, trivial reasons.”
In the meantime, Sánchez-Bayo is calling for more research to be done. “We didn’t expect to cause such a splash, but I’m glad we have done it because now the whole world can wake up to the fact that we have a problem,” he says. “We can see that the trend is worldwide. We don’t have enough data — we acknowledge that … We encourage everyone who has data hidden somewhere in their cupboard, please bring it out, write it up, so we can all see it and we can assess better.”
