Standford scientists have warned that an ‘alien invasion’ is underway in the US that could leave a path of destruction across the country.
The team identified 70 alien species of earthworms, imported from Asia, Europe and South America, that pose a threat to the ecosystem.
The invasive species consume more above-ground leaf litter than earthworms native to North America, which could destroy plants and starve amphibians and insects.
The alien earthworms make up 23 percent of the continent’s 308 native species – more than any other imported animal ever recorded.
The maps show how the alien earthworm population is dramatically spreading every twenty years
The alien species, as the researchers called them in their new study, has been largely overlooked because of the positive effects earthworms have on farmers’ and gardeners’ crops.
That’s because they form tunnels of air, water and nutrients that crops need to thrive, while their waste also serves as rich fertilizer.
Researcher combined the data with documents from alien earthworms intercepted at the US border between 1945 and 1975.
Using machine learning, the team combined the two databases to map where alien earthworms came from and how they spread across the US
The resulting dataset provided a view of the estimated number of non-native species versus the total number of both native and non-native earthworm species, using data from 2000 to 2021.
The team then gathered data on both species in 2,510 geographic areas in North America and broke them down to look at the name of the species, the area and date of their sighting, and the characteristics of the surrounding habitat.
Their findings showed that the alien earthworms are found in 97 percent of North America’s soils and represent 23 percent of earthworm species.
The jumping worm, also called Amynthas spp. is one of the invasive species that has invaded Washington, DC and killed plants and trees by sucking nutrients from the soil.
The jumping worm is one of 70 non-native species that can wreak havoc on North America’s ecosystem by altering soil nutrients, pH and texture, which can lead to poorer crop quality.
Researchers collected information about interceptions of alien earthworms at the US border between 1945 and 1975. They documented how the species arrived, the weather by plane, ship, car or some other unknown mode of transportation.
Alien species were brought to North America from all over the world. The researchers noted how many species were brought to North America from each continent and the total number of species now found in the US, Canada and Mexico.
Alien earthworms are more common in Canada, where the population is three times that of native earthworms, while in the lower 48 U.S. states and Mexico there is only one alien earthworm for every two native earthworms.
‘These ratios are likely to increase as human activities promote the development of alien species that threaten native earthworm species, a phenomenon that remains largely overlooked’ said Jérôme Mathieu, lead author of the study and associate professor of ecology at the Sorbonne.
Alien earthworms are mainly distributed when people trade them as fishing bait or for vermicomposting – turning organic waste into fertilizer.
Canada exports more than 500 million alien earthworms every year to other countries, mainly the US.
Researchers have created a map of where alien earthworms are mainly located, and the colors indicate the proportion of alien species in the area compared to native earthworms
One of the main concerns about alien earthworms becoming widespread in North America is their diet, researchers said in the study.
Native earthworms feed mainly in and on soil, but the non-native species feed on and on litter, indicating that they increase litter decomposition.
Non-native earthworms in deciduous forests in the US and Canada put pressure on trees – such as sugar maples – by altering soil microhabitat, allowing invasive plants to spread.
The additional increase in litter decomposition – the breakdown of organic matter – could lead to changes in ecological function and biodiversity.
This collapse has already led to a decline in the salamander population in the northeastern parts of the US, according to the study.
It added that alien earthworms can also change soil nutrients, pH and texture, leading to poorer crop quality despite increasing crop productivity.
Researchers suggest policymakers change current laws surrounding the spread of alien earthworms by encouraging people to switch to using native worms for composting and fishing bait.
More research is needed to understand the full effect of alien earthworms on the ecosystem.
“This is most likely the tip of the iceberg,” says co-author John Warren Reynolds of the Oligochaetology Laboratory and New Brunswick Museum in Canada.
‘Many more soil organisms may have been introduced, but we know very little about their consequences.’