As North Americans have busied themselves about their various concerns, unseen invaders have slowly been amassing beneath their feet. There are now more alien species than native species of earthworms in most places on the continent, a study聽has found.
鈥淥ur results reveal that the entire continent is being invaded by non-native earthworms through a variety of pathways,鈥� at the Sorbonne University in Paris and his colleagues write. 鈥淭hese aliens鈥� represent a major threat to native ecosystems.鈥�
Invading worms are a problem all over the world, but especially in North America, where many northerly areas have been free of earthworms since the last glacial period ended about 12,000 years ago. The study reveals just how massive the problem is. The team drew together more than 68,000 records from 1850 to 2021 to create a comprehensive overall picture of this silent invasion.
Advertisement
Alien worms are now found in 97 per cent of the areas for which there are records, whereas native species are found in just 72 per cent.
In terms of the proportion of non-native to native species, earthworms are the most invasive type of animal, the study says. Of the 308 earthworm species recorded in North America, 23 per cent are non-native. In Canada, invasive earthworms make up 77 per cent of the species.
The alien species also have much bigger ranges than most native species. 鈥淎 startling twelve of the thirteen topmost widespread earthworm species are alien,鈥� the researchers write.
We didn鈥檛 have a detailed picture of which non-native species are where before this study, says at the German Centre for Integrative Biodiversity Research.
鈥淭his is very important work,鈥� he says. 鈥淚t鈥檚 very impressive.鈥�
Non-native worms not only alter underground ecosystems, he says, they also affect ecosystems above the soil.
Earlier this year, Jochum鈥檚 team reported that in a forest in Canada, . Other studies have shown that invasive worms can cause declines of some plants and even (Acer saccharum).
鈥淭hese below-ground invaders also have impacts on above-ground communities,鈥� he says. 鈥淛ust because we don鈥檛 see them does not mean they don鈥檛 have a huge impact.鈥�
The spread of non-native worms in northern regions of the continent is being made worse by global warming, says Jochum. 鈥淲ith thawing permafrost and other changes, the problem will only increase, and maybe quite dramatically,鈥� he says.
The impacts aren鈥檛 all bad. Earthworms can dramatically increase crop productivity, says Mathieu鈥檚 study, and earthworm collecting for fishing bait, say, is a sizeable business in Canada.
There is little that can be done in areas where the worms have already arrived. 鈥淚t is virtually impossible to remove established populations of alien earthworms,鈥� write Mathieu and his colleagues.
However, the worms naturally spread slowly, by just 10 or so metres a year. It is human activities such as carrying soil or plants around that enable them to disperse much faster.
So measures such as cleaning hiking boots and car tyres, and not discarding unused bait worms, would help keep the non-native worms out of places they haven鈥檛 reached. The problem is that there is little awareness of the issue, says Jochum.
鈥淢any people I have met in Canada aren鈥檛 aware that the earthworms don鈥檛 belong,鈥� he says.
Mathieu declined to discuss the new study鈥檚 findings ahead of publication in a journal.
Reference: bioRxiv, DOI:
Hear more about this story on the 快猫短视频 Weekly podcast
