The study authors say that along with climate change, land use change and pesticides, earthworm infestations can be a “devalued guide” to a widespread decline in insects that some scientists have sounded the alarm for. Invasive earthworms have already been linked to changes in soil organisms, plant communities and the ability of forests to store carbon. So Malte Jochum, who led the new study in a poplar forest west of Calgary, expected the worms to have some effect on insects. However, he was “surprised” by the magnitude of the impact, said Jochum, a biologist and ecologist at the German Center for Integrated Biodiversity Research and the University of Leipzig. Researchers studying the impact of earthworms are returning from the woods at Barrier Lake Field Station at the University of Calgary, with Barrier Lake and Mount Baldy in the background. (Malte Jochum)
In areas with the largest earthworm masses, there were on average 61 percent fewer individual insects, 18 percent fewer species and 27 percent less total insect masses, the researchers said. reported this week in the journal Biology Letters. While competition for food and habitat clearly played a role for some organisms, ripple effects could be seen through the food web, even between organisms without a known predator-predecessor relationship or a competitive relationship with earthworms. “It’s fascinating how underground invasions can have such an impact on surface animals,” Jochum said. Earthworm infestations are widespread on the continent and increase in the north as permanent frost thaws. “Its scale is enormous and will likely expand with climate change,” said Jochum. He noted that there is no reason to believe that other ecosystems invading earthworms would react differently. And he believes that it is something that people should be careful while gardening or fishing, possibly transporting worms to new places. “It seems that people living in North America do not know that earthworms do not belong there; and I think it is always important to remind people of that.”

How the earthworm invasion began

During the last ice age, much of North America was covered by a huge layer of ice. When the glaciers receded, organisms such as insects and plants began to colonize again, explains Ed Johnson, an emeritus professor at the University of Calgary who co-authored the study. “The system has been reorganized without [earthworms]”And when they do appear, the system is reorganized.” This is a typical poplar forest in the study area above Lake Barrier, Kananaskis, Alberta. Bureaucracy on the tree marks one of the study plots. (Malte Jochum)
Researchers first observed earthworms invading the poplar forest surrounding the University of Calgary on-site station in the 1980s, Johnson said. It is suspected to have been in the area – the Kananaski Valley in the rocky foothills of Lake Barrier – since the 1960s. fishing spots or places where horses have been brought – a sign that people have brought them. For decades, generations of researchers have watched and watched the invasion. “Sometimes you can literally see it” in the changes in the leaf sand, Johnson said.

The “Ghostbusters engine” and how the study was done

When Jochum joined the project, he came up with some experience studying small creatures such as insects and was curious to see what the effects of earthworms might be on the ground. The researchers decided to look at square plots in the forest with slender trees such as poplar and poplar, many with signs of being scratched by bears. They sucked small creatures, from deciduous to spiders from the dense undergrowth filled with dead wood, using a vacuum carried like a backpack. Jochum describes it as “the Ghostbusters”. Pupil Romy Zeiss, co-author of the new work, uses the insect suction sampler, which was used to collect all the insects in a given sampling area. (Malte Jochum)
They also measured earthworms in the soil below for comparison by pulling them with an irritating mustard solution. Where there were more worms, there were significantly fewer insects in number, species and mass. “I was amazed at the strength and seriousness,” said Jochum. As expected, insects competing with earthworms for rotten organic matter were negatively affected. But there were few winners – predators like spiders and parasites. Why they increased in number as earthworms invaded remains a mystery that needs to be solved. The study was funded by the European Research Council and the German Research Foundation.

What does this mean for people fishing and walking in the forest

Carol Frost, an assistant professor and insect and spider ecologist at the University of Alberta, said the study addresses a “super-interesting question”. However, she knows from her own research on the effects of invasive species that this type of study is quite difficult, because so many variables can affect the results, from altitude to vegetation types in a given plot. He would like to see the study repeated in other places with earthworm infestations. Joann Whalen, a professor and soil scientist at McGill University who has researched earthworms in southern Quebec and discovered many of the same species, said she was intrigued by the study’s findings. “I think there are some lessons to be learned from this study,” he said. “If we do not pay attention and let earthworms enter new habitats, they will cause some changes that are quite dramatic and have very unexpected consequences.” Fishermen who use earthworms as bait can introduce them to new, remote areas they have not inhabited before. The researchers urge the public to be careful not to let the worms escape to the ground. (Emily Rendell-Watson / CBC)
He said that many people believe that earthworms are beneficial, but this shows another side and suggested that it might be worth raising public awareness. Dezene Huber, a professor of ecosystem science and management at the University of Northern British Columbia who studies the impact of disturbances such as fires and climate change on the biodiversity of insects and spiders, agreed. “I think it should really drive home; the fact that we really have to work trying to keep earthworms away from those areas where they have not already invaded.”