Gardeners revere earthworms for their ability to nourish soil. Scientific evidence confirms this affection. Research has shown, however, that earthworms may not be as friendly to us in the future due to climate change and their access to newly defrosted soils.
Earthworms have been viewed as pests in the past, along with slugs and sluglets. They were thought to be eating flower and vegetable roots below the soil’s surface. Earthworms were removed from gardens and killed until naturalists such as Charles Darwin proved their value.
Earthworms, also known as the “Darwin plough”, naturally till soils and increase their fertility by pulling the leaves underground to rot.
Earthworms can also be considered ecosystem engineers – species that have a large impact on their environment. They perform many activities that benefit us. These include the drainage, aeration, and formation of soils. Birds and mammals also enjoy a high-protein diet from them.
The feathered friend’s favourite. Jack Blueberry/Unsplash CC-BY-SA
They now have a dark side, which some may perceive.
Globetrotters with no feet
Earthworms from Europe, like the well-known “lobworm” ( Lumbricus terrestris), are found all over the world. They were transported by colonists to new lands in the soils of fruit-bearing and crop plants. This was seen on newly plowed farms as a bonus, and the worms increased food production.
In recent years, introduced earthworms established themselves in natural habitats such as temperate forests in North America. Most often, they arrive in these forests as fishing bait. The earthworms’ tendency to bury leaves and till soil has created problems. They have altered the soil’s nutrient content, exposed tree roots, and reduced cover for ground-nesting birds.
In such ecosystems, earthworms are considered invasive alien species. In the boreal forest of Arctic and subarctic Canada, a greater problem is emerging.
Arctic soils store about half of all carbon stored in soil globally. Forest fires were always thought to pose the greatest threat to carbon storage in boreal forests. Could be increasing due to rising temperatures.
Earthworms could be just as dangerous. When land that has been covered in ice or semi-permanently frozen thaws out, microorganisms as well as soil-dwelling creatures can access the carbon-rich nutrients.
A permafrost cellar in Alaska is now being flooded by meltwater. EPA-EFE/Jim Lo Scalzo
Earthworms are not present in the soils of northern regions after the last ice ages. Under normal conditions, these creatures would only spread 10 meters per year through the soil. Even if they survived, it is unlikely that they would reach northern regions.
But by building roads and pursuing recreational activities like freshwater angling, people are accidentally transporting ecosystem-engineering earthworms into areas where recently defrosted soil awaits. It is again abandoned living bait from fishing that opens a new front of invasion.
Earthworms release carbon dioxide into the air by exercising their natural behaviour. In 2015 published a study that predicted losses of up to 10g per square metre per year. This is similar to the amount of carbon released from wildfires and the removal of timber.
Earthworms are not as hardy as you might think. Some, like the octagonal earthworm ( Dendrobaena Octaedra), can survive freezing temperatures, and their eggs can withstand temperatures down to -35degC. Some earthworms, like the lobworm, can burrow deeply to survive temperatures below freezing. Once established, these species are difficult to eradicate.
The lobworm is now found worldwide. It was once restricted to Western Europe. Liz Weber/Shutterstock
Earthworms interact with microorganisms in these newly available soils. This allows them to decompose plant material that was previously frozen in ice and generate large amounts of carbon dioxide, methane, and other greenhouse gasses.
The further release of greenhouse gasses accelerates the temperature increase. This is likely an unstoppable phenomenon, and the best way to deal with earthworms would be to prevent them from accidentally spreading to other sites in the subarctic region through education and possibly by policing recreational areas.
In most soils, earthworms are essential, but at extremely northern latitudes, our perception of these animals has changed dramatically. We, the public, government, industry, and scientists, must address global issues related to the climate crisis, which affects us, earthworms and all life on Earth.