Vox - Brian Resnick
When insects go extinct, other species follow.
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“Help.”
Brice Nihiser/Barcroft Images/Barcroft Media via Getty Images
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Insects are the most abundant animals on planet Earth. If you were to put them all together into one creepy-crawly mass, they’d
outweigh all humanity by a factor of 17.
Insects outweigh all the fish in the oceans and all the
livestock munching grass on land. Their abundance, variety (there could
be as many as 30 million
species),
and ubiquity mean insects play a foundational role in food webs and
ecosystems: from the bees that pollinate the flowers of food crops like
almonds to the termites that recycle dead trees in forests.
Insects are also superlative for another, disturbing reason: They’re vanishing at a very fast rate in some parts of the world.
“The pace of modern insect extinctions surpasses that of vertebrates by a large margin,” write the authors of an alarming new
review in
Biological Conservation of
the scientific literature on insect population declines published in
the past 40 years. The state of insect biodiversity, they write, is
“dreadful.” And their biomass — the estimated weight of all insects on
Earth combined — is dropping by an estimated 2.5 percent every year.
In all, the researchers conclude that as much as 40
percent of all insect species may be endangered over the next several
decades. And around 41 percent of all insect species on record have seen
population declines in the past decade. Most of the data was obtained
from studies conducted in Europe and North America. However, of the
world’s insect species live in the tropics, where new species are still
being discovered. A true, global assessment might tell a different
story. The authors note that there’s not enough data from tropical
regions.
(Update: It turns out there’s another big caveat to the
new data trove. As University of New England ecologist Manu Saunders
pointed out in a
blog post, though the intent of the authors of the
Biological Conservation
paper was to “compil[e] all long-term insect surveys conducted over the
past 40 years that are available through global peer-reviewed
literature databases,” in fact, they limited their search just to papers
that included the terms “insect,” “declines,” and “survey.”
The
trouble with this method is that it biases the analysis toward
declines, and excludes gains or stable populations. “‘Survey,’” writes
Saunders, “is just one term that could pick up long-term studies.” Which
means the paper is not an absolute reckoning of insect declines.)
“It is evident that we are witnessing the largest
[insect] extinction event on Earth since the late Permian and Cretaceous
periods,” the study authors write. Given their limited research
methods, this might be a premature conclusion. But there are reasons to
be worried about insects, particularly vulnerable orders, like
butterflies. And human activity is hugely to blame.
Bees, butterflies, moths, dung beetles, and crickets are all declining
Butterflies and moths, known as the Lepidoptera order,
are some of the hardest hit: 53 percent of Lepidoptera have seen
declining population numbers, according to the new survey.
This is especially concerning as butterflies, which are very sensitive
to changes in landscape and food sources, are often a bellwether of
environmental health.
Some 50 percent of Orthoptera species (grasshoppers and
crickets, another important source of food for an enormous array of
animals) are also in decline. Forty percent of bee species are listed as
vulnerable for extinction, and most dung beetle species (named for —
you guessed it — what they like to eat) are vulnerable or endangered.
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| Biological Conservation |
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| Biological Conservation |
This new study paints a picture of a problem that’s been recorded in individual ecosystems. A 2017
study
in Germany noted a 75 percent decline in flying insects over three
decades. “The widespread insect biomass decline is alarming,” the
authors wrote, “ever more so as all traps were placed in protected areas
that are meant to preserve ecosystem functions and biodiversity.”
What’s “most worrying,” the authors write, is that the
losses seem to impact both “specialist” insects and “generalist”
insects. A specialist is an organism that occupies a tiny niche in an
ecosystem (like a moth that only feeds on one particular plant). A
generalist, on the other hand, is more adaptable and can more easily
change environments and food sources.
Both
types of insects are facing major losses. “This suggests that the
causes of insect declines are not tied to particular habitats, but
instead affect common traits shared among all insects,” the study
authors write.
What’s killing all the insects?
The state of insect biodiversity is “dreadful” because we
know what happens when ecosystems lose insects: They lose other species
as well.
In October, a study in
Proceedings of the National Academy of Science documented
that between 1976 and 2013, the number of invertebrates (like insects,
spiders, and centipedes) in the Luquillo rainforest in Puerto Rico
caught in survey nets plummeted by a factor of four or eight. When
measured by the number caught in sticky traps, invertebrates declined by
a factor of 60. And that loss of insects coincided with losses of
birds, lizards, and frogs. “The food web appears to have been
obliterated from the bottom,” the Washington Post’s Ben Guarino
reported on the study.
So what’s happening?
The researchers in the new
Biological Conservation paper outline four broad, global problems leading to insect loss. They won’t surprise you.
- Habitat loss as a result of human development, deforestation, and the expansion of agriculture
- Pollution, particularly via pesticides, fertilizers, and industrial wastes
- Parasites and pathogens — like the viruses that attack honeybees — and invasive species
- Climate change
In summary: Human activity is to blame.
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“Habitat restoration, coupled with a drastic reduction in agro-chemical
inputs and agricultural ‘redesign’, is probably the most effective way
to stop further declines,” the researchers write, with “redesign”
meaning making agricultural plots more hospitable to the native insects
(for instance, maintaining flowering plants for pollinators to feast
on). Pesticide use needs to decline drastically as well. “Unless we
change our ways of producing food, insects as a whole will go down the
path of extinction in a few decades,” the researchers write.
And if we don’t act, the researchers give a stark warning:
The repercussions this will have for the
planet’s ecosystems are catastrophic to say the least, as insects are at
the structural and functional base of many of the world’s ecosystems
since their rise at the end of the Devonian period, almost 400 million
years ago.
With so much devastating and widespread loss of insects —
and other forms of life — it’s hard to say where we should focus our
attention. In
Science, Jonathan Baillie, the chief scientist at
the National Geographic Society, and Ya-Ping Zhang, the vice president
of the Chinese Academy of Sciences,
argued that half of all land should be protected for wildlife by 2050, to give plants and animals a chance to thrive.
This is a lofty, perhaps unrealistic goal. But we’ve
taken so much from wildlife. We need to think more about how to stop
taking environments away from plants and animals. “Simply put,” Baillie
and Zhang
write in
Science, “there is finite space and energy on the planet, and we must decide how much of it we’re willing to share.”
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