Earthworms – beneficial, dangerous and endangered

Earthworms, though not among the most popular animals, are silent heroes of natural ecosystems and gardens. By digging their tunnels, they enrich the soil with nutrients and aerate it, improving conditions for plant growth. Usually, we are unaware of their presence beneath our feet, but sometimes they emerge en masse, and some can even jump! What is worth knowing about the life of earthworms?

Why do earthworms come out after rain?

Earthworms spend most of their lives in underground tunnels. This is possible thanks to a special breathing technique that involves gas exchange through the surface of their slimy skin. Maintaining an appropriate level of moisture is crucial for this process to occur effectively – oxygen penetrates the worm’s body, while carbon dioxide is released.

However, when heavy rain starts, underground conditions become far from ideal. As explained by scientists from Penn State University, excess water reduces the permeability of the soil, putting earthworms at risk of suffocation, especially when some tunnels become completely flooded. While emerging on the surface during sunny days poses the risk of drying out, during rain, earthworms can freely take advantage of abundant oxygen and moisture.

An alternative, though not mutually exclusive, explanation is that the sound of falling rain may resemble the presence of predators, such as moles, prompting earthworms to escape upward to save their lives.

Earthworms as villains

About 7,000 species of earthworms have been identified worldwide. However, some of them cause more harm than good. In North America, 70 foreign, highly invasive species have been observed, successfully taking over ecosystems and threatening local biodiversity.

Particularly dangerous are so-called jumping worms (Amynthas agrestis) originating from Japan and the Korean Peninsula. Their adaptability to different conditions and rapid reproduction are as concerning as their innate voracity. Asian earthworms consume massive amounts of leaf litter, harming nearby plants and small invertebrates living in the topsoil. Well-fed, they become so energetic that they can leap up to 30 cm above the ground – a trait that earned them their common name.

According to scientists from Stanford University, invasive earthworms already pose a threat to American sugar maples, leading to a cascade of negative consequences for the food chain. Paradoxically, organisms praised for improving soil health can, in foreign environments, alter pH and nutrient availability to the detriment of local organisms.

Climate change and earthworms

Changes in the underground world are not only caused by unwanted imports. According to scientists, advancing climate change also affects earthworm populations and, consequently, soil quality.

Extreme temperatures are particularly problematic – below 10°C, earthworms reduce their activity, and above 40°C, they stop reproducing altogether. If we add droughts to heatwaves, the future existence of beneficial earthworms in many regions of the world is under threat. Cooler zones, however, could benefit from global warming, provided that increased temperatures are accompanied by sufficient rainfall.

Depending on the intensity of precipitation in the coming years, invasive earthworms in North America could either gain further momentum for development or face a natural slowdown. On the other hand, increasing episodes of prolonged droughts and sudden floods threaten native earthworm populations worldwide.

In the end, human efforts may prove critical – observations show that sustainable agricultural practices and initiatives supporting biodiversity can mitigate the negative effects of climate change on earthworms. With mutual benefits, no less!