Dr. Malte Jochum, first author of the study, digging for invasive earthworms in the forest above Barrier Lake, Kananaskis Valley, Alberta.Felix Günther/Supplied
Though earthworms might serve many a helpful purpose in our gardens and composts, the same cannot be said for their presence in some of Canada’s forests. Just ask the bugs.
A recent study conducted in an aspen forest near Barrier Lake, Alta., found that insect populations had dropped significantly as a result of an overabundance of earthworms — an invasive species in North America. Published in Biology Letters, the researchers found that in areas with the highest mass of earthworms, there were 61 per cent fewer individual insects, 18 per cent fewer insect species and a 27 per cent reduction in the total mass of insects on average.
“There has been a field station in the area since the 1980s, observing how the earthworms had begun to overpopulate the forest,” said Dr. Malte Jochum, a biologist at the German Centre for Integrative Biodiversity Research and the University of Leipzig. “We knew they were impacting the forests in many ways, but I was surprised by how strongly they were affecting the insects.”
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The findings contribute to a growing body of research raising the alarms on declining insect populations in Canada within the past few decades. Nevertheless, the story on bugs is more complicated than a simple drop in the number of insects. It is also about the intersection of climate change and a host of other threats, as well as the greater potential risk to insect diversity. The “insect apocalypse,” as it’s been dubbed, might need to be re-characterized as yet another branch of Canada’s biodiversity crisis.
Findings showed that earthworms are a formidable foe for many insects when it comes to food and habitat resources in the studied forest, said Dr. Jochum, particularly those that must compete with them to eat the dead plant and animal material found on forest floors. However, earthworms were also found to be a threat to branches of the food chain to which they had no direct predator-prey or competitive relationship, including animals, plants and other organisms reliant upon certain insects for food or habitat.
Malte Jochum collects samples of arthropods with a suction sampler.Olga Ferlian/Supplied
In order to count how many insects and worms were in a given area, Dr. Jochum and his team had two main methods at their disposal — a “Ghostbusters-like” vacuum and a mustard solution. The vacuum, carried by Dr. Jochum and his team like a backpack, was used to suck a variety of insects from the forest’s undergrowth and debris. The worms, on the other hand, were drawn out by spraying a mixture of mustard powder and water on the soil, and were counted by the researchers once they reached the surface.
“It doesn’t hurt the worms,” he clarified. “They just find it a bit… irritating.”
Given the helpful role they play in agriculture, it is easy to forget earthworms are both invasive in and harmful to forest environments, said Colin Cassin, a policy manager at the Invasive Species Centre who has studied the impacts of earthworms in southern Ontario. After their disappearance from North America during the last ice age thousands of years ago, they were reintroduced by European colonizers in the 1800s and spread through farming and fishing equipment.
Members of the EcoWorm team hike back from forest plots to the University of Calgary's Barrier Lake Field Station.Malte Jochum/Supplied
“In Ontario, 18 of our 20 earthworm species meet the threshold of being considered invasive,” said Mr. Cassin. The case of earthworms impacting insect populations in Alberta is also unsurprising, he added, given the impacts they’ve had on ecosystems and organisms across the country. And as climate change drives temperatures up farther north, things could get worse.
According to Dr. Jochum, if the permafrost in northern Canada were to melt and its soils became habitable for earthworms, these environments could see invasions similar to that of Barrier Lake’s forests, adding an additional stressor to plants and animals already dealing with the consequences of climate change and human land use on their immediate environments.
Though many may be inclined to point to Dr. Jochum’s study as an example of an increasing decline of insect populations worldwide — the insect apocalypse — others would consider this inaccurate, including Dr. Jeremy Kerr, research chair in macroecology and conservation at the University of Ottawa. For him, earthworms’ impacts on insect numbers is just one detail of the current state of bug-related affairs worldwide — one that is better described as part of the general biodiversity crisis experts have observed over the past several decades, linked to both climate change and a myriad of other factors, depending on the specific ecosystem.
“Insects are in trouble,” he said, “but the trouble they are in is comparable to the kinds of challenges other animals face. My experience in speaking with ecologists and conservation biologists is that I have yet to meet one who thinks that we’re in the middle of an insect apocalypse.”
The narrative that insects are dying off at a uniquely alarming rate stems from a study published in PLOS One in 2017, which found a 75-per-cent reduction in the biomass of insects in certain protected localities of southern Germany. Given the highly localized nature of the study, said Dr. Kerr, it is impossible to apply its findings on a global scale — as many at the time did — and no concrete evidence has been presented since that indicates that insects are at a greater risk than any other animal.
Status of native species in selected
groups, Canada, 2015
The risk of extinction faced by insect species is on par with that of most other organisms in Canada.
Extinction risk levels:
Presumed extinct
Vulnerable
Percentage
of species
with known
risk levels
Possibly extinct
Apparently
secure
Critically imperiled
Secure
Imperiled
0
20
40
60
80
100%
Reptiles
96%
Corals
30
Amphibians
100
Vascular plants
99
Mammals
96
Dragonflies and damselflies
98
Bees
56
Birds
96
Fishes
50
Moths and butterflies
40
Beetles
51
Mosquitoes
84
0
20
40
60
80
100%
THE GLOBE AND MAIL, SOURCE: CANADIAN
ENDANGERED SPECIES CONSERVATION COUNCIL
Status of native species in selected groups,
Canada, 2015
The risk of extinction faced by insect species is on par with that of most other organisms in Canada.
Extinction risk levels:
Presumed extinct
Vulnerable
Percentage
of species
with known
risk levels
Possibly extinct
Apparently secure
Critically imperiled
Secure
Imperiled
0
20
40
60
80
100%
Reptiles
96%
Corals
30
Amphibians
100
Vascular plants
99
Mammals
96
Dragonflies and damselflies
98
Bees
56
Birds
96
Fishes
50
Moths and butterflies
40
Beetles
51
Mosquitoes
84
0
20
40
60
80
100%
THE GLOBE AND MAIL, SOURCE: CANADIAN ENDANGERED
SPECIES CONSERVATION COUNCIL
Status of native species in selected groups, Canada, 2015
The risk of extinction faced by insect species is on par with that of most other organisms in Canada.
Extinction risk levels:
Presumed extinct
Vulnerable
Percentage
of species
with known
risk levels
Possibly extinct
Apparently secure
Critically imperiled
Secure
Imperiled
96%
Reptiles
30
Corals
100
Amphibians
99
Vascular plants
96
Mammals
Dragonflies and
damselflies
98
56
Bees
96
Birds
50
Fishes
Moths and
butterflies
40
51
Beetles
84
Mosquitoes
0
20
40
60
80
100%
THE GLOBE AND MAIL, SOURCE: CANADIAN ENDANGERED SPECIES
CONSERVATION COUNCIL
While some insects may be suffering in numbers in some parts of Canada, said Dr. Kerr, some might be thriving in other parts of the country, existing just as before or even overtaking ecosystems as invasive species. When it comes to the disappearance of insects, it’s not necessarily the sheer number of insects researchers and conservationists should be watching out for, but the diversity of species within a given ecosystem, as well.
“Common species may become more common, and rare species may become more rare as a consequence of human disturbance,” he said. “This is the process that’s intrinsic to a lot of what we think of as modern-day extinction, and it’s our job to try and hold onto the species we share the planet with.”
Part of holding onto those species includes working to undo some of the harm humans have caused Earth’s ecosystems — or at least, making an active effort to prevent them from getting worse, said Dr. Jochum. In the case of invasive earthworms, while there may not be much ecologists can do once the worms have infested a forest, humans should work towards ensuring they don’t spread further. Raising awareness on the risks they pose to wild animal and plant species by encouraging hikers to check their boots and tires for worms before venturing into new forests, and reminding fishers not to dump their bait after they are finished using it are important steps in the war against earthworms, he said. However, policymakers also need to consider earthworms when managing natural ecosystems, which includes taking care to ensure developers are mandated to implement checks-and-balances that consider potential earthworm spread.
“Earthworms are good for the garden, but bad for the forest,” said Mr. Cassin. “We need to starting thinking about the negative consequences of their presence if we’re going to conserve what they’ve put at risk.”
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