Alien Invasion: Non-native earthworm species threaten US ecosystem, warn Stanford scientists

Researchers at Stanford University have identified up to 70 non-native earthworm species in the US that could have devastating ecological consequences. These invasive species consume more aboveground leaf litter than native worms, potentially destroying plants and impacting insects and amphibians.

Alien Invasion: Non-native earthworm species threaten US ecosystem, warn Stanford scientists

THE ballooning population of non-native "alien" earthworm species in the United States could pose significant ecological consequences, scientists at Stanford University have warned, DailyMail reported. As many as 70 different types of earthworms native to Asia, Europe and South America have been identified as potential threats, it said.

The identified earthworms consist of 23 percent of the 308 species in North America and consume more aboveground leaf litter than their native counterparts. This excessive consumption could destroy plants and cause a ripple effect by starving insects and amphibians, the scientists warned.

Historical Perspective

To understand the invasion's origin and spread, researchers combined records of intercepted alien earthworms at the US border from 1945 to 1975 with machine learning techniques. The resulting dataset, using information from 2000-2021, revealed that these invasive species currently reside in 97 per cent of the soil across North America.

The jumping worm, or Amynthas spp., is one such invasive species that has already caused damage in Washington, DC, killing plants and trees by draining essential nutrients from the soil. While alien earthworms are more widespread in Canada, the US and Mexico face a growing threat due to human activities facilitating the development of these invasive species.

Initially, the introduction of these earthworms was overlooked due to their positive impact on crops for farmers and gardeners, by creating tunnels containing air, water, and nutrients essential for crop growth. Additionally, their waste acts as a valuable fertilizer.

Human Activities and Trade

The primary mode of distribution for alien earthworms is through human activities such as trading them as fish bait or for vermicomposting. Canada annually exports over 500 million alien earthworms to various countries, particularly the US, contributing to the spread of these invasive species.

The study highlights concerns about the dietary habits of alien earthworms, primarily feeding on litter, which can lead to increased litter decomposition. This alteration in ecosystems, particularly in broadleaf forests in the US and Canada, is stressing trees and impacting biodiversity.

Current Scenario and Future Recommendations

Researchers emphasise the need for policymakers to reevaluate laws surrounding the distribution of alien earthworms. They suggest encouraging the use of native worms for composting and fish bait to mitigate the impact on ecosystems. However, more research is required to fully understand the extent of the effects of alien earthworms on the environment.

Jérôme Mathieu, lead author of the study and an associate professor of ecology at the Sorbonne, warns that the current situation is likely just the beginning, and urges further research to look at the impact on other soil organisms and the broader ecosystem. "These ratios (number of non-native earthworms vs native species) are likely to increase because human activities facilitate the development of alien species that threaten native earthworm species, a phenomenon still largely overlooked," he said.

"This is most likely the tip of the iceberg. Many other soil organisms may have been introduced, but we know very little about their impacts," study John Warren Reynolds of the Oligochaetology Laboratory and the New Brunswick Museum in Canada, who co-wrote the paper.