A new study suggests that 40 percent of insect species are in decline, a
sobering finding that has jarred researchers worldwide.
Rocky Mountain locusts once gathered in such large numbers that they blotted
out the sun over the Great Plains, rivalling the famous bison herds in size and
appetite. In the summer of 1875, for example, a swarm of around 10 billion
locusts took nearly a week to pass through Plattsmouth, Nebraska.
New research shows that large-scale declines in insects, while perhaps less
dramatic, are by no means a thing of the past—and that insects may be more vulnerable
than we thought. A study published recently in the journal Biological
Conservation made headlines for suggesting that 40 percent of all insect
species are in decline and could die out in the coming decades
Why it matters
“There is reason to worry,” says lead author Francisco Sánchez-Bayo, a
researcher at the University of Sydney in Australia. “If we don’t stop it,
entire ecosystems will collapse due to starvation.”
The paper, the first global survey of research on insect populations around
the world, singles out a few groups of critters that are particularly
threatened: moths and butterflies; pollinators like bees; and dung beetles,
along with other insects that help decompose feces and detritus.
The study follows several high-profile papers on insect declines that
shocked even experts in the field. In October 2017 a group of European
researchers found that insect abundance (as measured by
biomass) had declined by more than 75 percent within 63 protected areas in
Germany—over the course of just 27 years.
A year later, two researchers published a paper in the Proceedings of
the National Academy of Sciences suggesting that within a relatively
pristine rainforest in Puerto Rico, the biomass of insects and other arthropods
like spiders had fallen between 10- and 60-fold since the 1970s.
The study found that half of the moth and butterfly species studied are in
decline, with one-third threatened with extinction, and the numbers for beetles
are almost exactly the same. Meanwhile, nearly half of surveyed bees and ants
are threatened. Caddisflies are among the worst off—63 percent of species are
threatened, likely due in part to the fact that they lay their eggs in water,
which makes them more vulnerable to pollution and development.
Why the decline?
There are a number of reasons why these animals are in trouble, and there’s
no single smoking gun, Wagner says. “I’m afraid the answer is that it’s
death by a thousand cuts.”
Factors behind the decline include, perhaps foremost among them, habitat
changes wrought by humans, such as deforestation, and
conversion of natural habitats for agriculture. In Europe and North America,
the decline of small family farms, known for open pastures, hedgerows, and
other areas where “weedy” plants like wildflowers can grow—areas that are
perfect for insects—has certainly played a part, Wagner adds, as has the
draining of wetlands and swamps.
Along with agriculture comes the use of chemicals like herbicides,
fungicides, and pesticides. Insecticides, unsurprisingly, hurt non-target
species, and neonicotinoids have been implicated in the worldwide decline of
bees. Pesticides may play a role in one-eighth of the species’ declines
featured in the study.
Climate change undoubtedly plays a big role as well, especially extremes of
weather such as droughts, which are likely to increase in intensity, duration,
and frequency in the future, Wagner says. Other factors include invasive
species, parasites, and diseases.
The impact of the decline
Insects serve as the base of the food web, eaten by everything from birds to
small mammals to fish. If they decline, everything else will as well,
Sánchez-Bayo explains.
They also provide invaluable “services” to humanity,
including plant pollination, says John Losey, an entomologist at Cornell
University. About three-fourths of all flowering plants are pollinated by
insects, as well as the crops that produce more than one-third of the world’s
food supply.
“No insects equal no food, [which] equals no people,” says Dino Martins, an
entomologist at Kenya’s Mpala Research Centre and a National Geographic Explorer.
Another service: waste disposal and nutrient cycling. Without insects like
dung beetles and decomposers breaking down and removing animal and plant waste,
“the results would be unpleasant,” says Timothy Schowalter, an entomologist at
Louisiana State University.
So just how dire is the situation for insects? Ultimately, while it’s
concerning, “we don’t really have the information yet to answer [that]
question,” Wagner says. That’s mainly due to a lack of long-term studies, but
insect abundance is also tough to study. Many of these animals have
boom-or-bust life cycles, which can take advantage of prime conditions to
explode. However, they’re also highly sensitive to fluctuations
in weather.
One definite result of recent studies is increased interest and funding for
long-term research, Wagner says. Such attention could help prevent extinctions
like the loss of the Rocky Mountain locust.
“Even insects that can seem very abundant can disappear over a short period
of time,” Schowalter says. “But unless somebody is watching or concerned,
nobody [will] prevent that.”
