Can Earthworms Drown? How They Breathe and Survive in Water
An earthworm's survival in wet environments depends less on the water itself and more on available oxygen. Explore the delicate balance they require to breathe.
Earthworms are a familiar sight in gardens and on sidewalks after a rainstorm, thriving in the dampness of the soil. Their appearance on the surface during downpours raises a common question. Given their need for a moist environment, it seems counterintuitive that they could be in danger from water, which leads to the query: can an earthworm actually drown?
How Earthworms Breathe
Lacking lungs or gills, earthworms use cutaneous respiration, breathing directly through their skin. Their entire outer surface is a respiratory organ covered in a thin layer of mucus, which is the medium for gas exchange. Oxygen from the surrounding air or water dissolves into this mucus before passing into the worm’s body.
Just beneath the skin lies a dense network of capillaries where oxygen is picked up by hemoglobin in the blood and transported. Simultaneously, carbon dioxide, a waste product, moves from the blood, across the skin, and out into the environment. This process relies on the skin remaining moist; a dry earthworm is unable to breathe and will suffocate.
Earthworms in Waterlogged Conditions
The same respiratory system that allows an earthworm to thrive in damp soil becomes a liability when that soil becomes saturated with water. During heavy rainfall, water fills the small air pockets that worms depend on for oxygen, creating a low-oxygen environment known as anoxia. Trapped in their burrows without access to sufficient dissolved oxygen, earthworms are at risk of suffocation.
To avoid this, they migrate upwards to the surface, which is why they are so commonly seen on pavements after a significant storm.
Survival Underwater
While waterlogged soil can be deadly, an earthworm can survive for some time fully submerged in a puddle or a container of water. Their ability to breathe through their skin allows them to absorb dissolved oxygen directly from the water. As long as the water is sufficiently oxygenated, they can continue to respire.
The duration of their survival underwater depends on water temperature and oxygen levels. Colder water holds more dissolved oxygen than warmer water, extending the time a worm can remain submerged. In a small, stagnant puddle, the available oxygen can be depleted quickly, whereas a larger or more aerated body of water could support them for longer.