Insect decline is a big—and mostly overlooked—piece of the biodiversity loss puzzle. Words & photos :: Leslie Anthony.
“If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos.”
So said eminent biological philosopher and author E.O. Wilson, an entomologist who specialized in ants (and coined the term “biophilia”). The quote resurfaced in a 2014 book by biologist Dave Goulson, the world’s foremost expert on the behaviour, ecology and conservation of bumblebees. In Goulson’s A Buzz in the Meadow, Wilson’s quote is a springboard both to declare that insects are vanishing worldwide, and to question our lack of concern.
Goulson contrasts the ramifications of no insects—i.e., potential global cataclysm—with something of far less consequence on which we expend much conservation capital: the ever-lovable panda, whose disappearance, while symbolic, might mean only “… a tiny bit more bamboo in a forest in China.”
His point: big, cute animals like pandas speak to our philanthropic instincts, while most insects—animals we barely notice—do not. Adjusting our attitude toward insects as a group would be a first step to taking their declines seriously. As winter moves into spring and another year of insect Armageddon looms, it’s an issue worth considering.
Fortunately, the insect world has its own pandas, and these do have our attention. Accelerating declines in wild pollinators like butterflies and bees, and annual losses of up to 80 per cent of hives of the yeoman European honeybee (employed in agriculture around the globe), have been big news. With pollinators required for reproduction in 90 per cent of flowering plants and three-quarters of crop species, worldwide declines raise the spectre of global food shortages. Beyond humans, fruits and seeds derived from insect pollination are on the menu for a quarter of all birds and mammals.
Big, cute animals like pandas speak to our philanthropic instincts, while most insects—animals we barely notice—do not.
But while pollinators’ important ecological roles were once familiar to most, times have changed: a study in Britain found one in five schoolchildren had never seen a bee in the wild; worse, half their parents didn’t know bees help pollinate crops. No surprise then that bee declines have sparked an industry of public-awareness initiatives and global citizen-science partnerships.
“People can tell a robin from a chickadee and numerous other birds, but when it comes to bees, they might only recognize honeybees and none of the 20,000 other species globally,” says Dr. Elizabeth Elle, a biologist at Simon Fraser University in Vancouver.
Elle researches the role of wild pollinators in threatened natural ecosystems as well as agricultural settings. She found that wild pollinators become more important to agriculture when there are natural landscapes nearby. This, however, also makes them more vulnerable to the negative effects of agricultural practices. Because bees supply their nests with pollen, they visit flowers more often than the wasps, beetles, flies, hummingbirds and untold other species that do so simply for food. As a result, bees are increasingly susceptible to the cumulative effects of anything nasty that might be in that pollen. Cue the much-discussed use of bee-killing neonicotinoid insecticides here.
“Our problems with honeybees have to do with how we raise and move them around, the pesticides we use and the diseases they carry,” notes Elle. “And yet wild pollinators are also in decline for reasons that are far less clear—though possibly related.” About 20 years ago, the Western bumblebee was considered the second most common bee in Vancouver-area blueberry fields. Not so today. “We didn’t see one for the first four years studying those areas,” says Elle, “then this year saw one.”
This same story—insert different crop or different bee—can be excavated anywhere. That was clear in a 2011 study by American researchers who compared current and historical abundance in wild North American bumblebees that showed four species had declined by up to 96 per cent. More notably, declining populations exhibited less genetic diversity and significantly higher pathogen loads than non-declining populations, to the extent the authors felt such metrics were “realistic predictors of these alarming patterns of decline.”
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While reasons for wild bee declines remain enigmatic, the precipitous downturn in monarch butterflies is sadly understood. As recently as the 1990s, a billion of the iconic orange-black “king of butterflies” migrated south each fall from central and eastern North America to overwinter in south-central Mexico. By 2014, only 56.5 million remained, a decline of more than 80 per cent from the 21-year average. Although the slide was linked to agricultural practices that decimated milkweed—the plant on which monarch eggs hatch and spend the larval stage—factors such as climate change, degradation of overwintering sites, pesticides, disease, predators and parasites all exert pressure on the species. With most of these issues ongoing, the milkweed deficit was merely a tipping point.
The importance of wild pollinators to natural ecosystems is underappreciated; when pollination breaks down, less food for everything leads to upwardly cascading changes everywhere in the food chain. “As a conservation biologist, I can tell you we know that insect species are being lost across the planet,” says Elle. “Are we seeing the same thing for insects with regard to biodiversity loss and the sixth great extinction? Yes. Are we recognizing insects as in particularly steep decline? No… but no one is really looking.”
If no one is looking at insects in general, how to judge broader patterns? Perhaps through something that depends on them—like birds, which indeed turn out to also be in steep decline (subject for another column). But while sudden changes in insect-dependent animal populations offer a research roadmap into some declines, what about cases of slow, steady attrition?
Walk the shoulder of any Ontario highway in summer and you’ll notice an unusual number of ants underfoot. Why? Because they’re enjoying a 24/7, all-you-can-eat buffet of insects killed by motor vehicles. One of few studies on this issue was carried out by a team from Sudbury’s Laurentian University led by Dr. James Baxter-Gilbert, on sections of Ontario’s Highway 400 that traverse the amphibious landscapes east of Georgian Bay.
Over two summers Baxter-Gilbert collected 117,000 road-killed insects during daily surveys of a two-kilometre stretch of highway. Though large, this number represents only a fraction of what was actually killed: Countless individuals were stuck to vehicles, obliterated on the pavement, too small to see or scavenged by animals like ants. The collection was dominated by Hymenoptera (bees, wasps, etc.), Lepidoptera (butterflies, moths) and Diptera (flies, mosquitoes, etc.). Fully a third were pollinators. “That might seem disproportionate,” notes Baxter-Gilbert, “but it makes sense when you think about who’s flying around at car level. We concluded insects are dying on roads in astronomical numbers—especially those super-important to ecosystems.”
What does astronomical mean? Even the most conservative estimates seem insane. Highway 400 is a medium-use road of 10,000 vehicles/day in an area of medium insect diversity. Extrapolating to the entire length of similar roads in North America, Baxter-Gilbert’s group came up with 10 billion Lepidoptera, 25 billion Hymenoptera and a staggering 60–190 billion Diptera deaths per year.
“We don’t know what these kinds of numbers mean,” notes Baxter-Gilbert. “We’re assuming 25 billion individuals is significant, however, we have no clue how much loss an ecosystem can sustain. Especially with pollinators.”
But does it matter? Maybe not, says Elizabeth Elle. “Just because we can’t put a finger on an exact cause of insect declines doesn’t mean they aren’t all important,” she says. “As Dave Goulson puts it, ‘If a middle-aged, out-of-shape, overweight guy dies from a heart attack, you don’t ask what killed him—it was, obviously, everything.’”
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