Earthworms stay underground when it rains because excessive moisture can drown them. They usually come out in dry weather to avoid this.
Many imagine that earthworms come to the surface when it rains to avoid drowning underground. This is not entirely accurate; worms breathe through their skin and therefore need a certain level of moisture, but they do not flee their burrows because of water. In reality, it is more about taking advantage of favorable conditions to move over longer distances without the risk of drying out. The moist soil allows worms to better explore new territories or find partners for reproduction. This behavior gives the impression that they come out because of the rain, while it is mainly a practical matter of humidity.
Earthworms primarily breathe through their skin, which is thin and permeable, and must remain constantly moist to allow oxygen to pass through. But be careful: too much moisture and water replaces the air present in the soil, which seriously hinders their breathing. Conversely, when the soil is too dry, their skin also dries out and gas exchanges become nearly impossible. Clearly, these little creatures seek a delicate balance, an ideal humidity: soil that is neither waterlogged nor desert-like, just soft and cool as they prefer.
Earthworms breathe through their skin, which makes them particularly vulnerable to a lack of oxygen if their environment is flooded with too much water. While humidity is essential for them, water saturation can block their breathing, exposing them to the risk of drowning. Forced to leave their burrow, they climb to the surface where various predators such as birds, frogs, and small mammals await them. Up there, their vulnerability increases significantly, as they lose the protection offered by their underground habitat. Without shelter or protective humus during these moments, they quickly become an easy snack.
Earthworms have several clever techniques to minimize risks during rainy periods. Since they become easy prey for birds or small mammals on the surface, they prefer to stay in their burrows and move as far away from the entrance as possible. When their tunnels fill with water, some take shelter in slightly higher areas, thus keeping a fairly dry space while carefully avoiding exposure. Those who are forced to come out generally remain still, as the slightest movement would betray their presence to predators lurking in the rain. And as soon as the weather becomes drier again, they quickly return to their underground shelters.
Earthworms love stable, shaded, and especially moist environments, but never too waterlogged. A calm environment without sudden changes allows them to dig their galleries, feed peacefully, and lay their eggs without stress. The surface, on the other hand, experiences constant fluctuations in temperature, humidity, and a high risk of being spotted by predators. You could say that going outside in the rain for an earthworm is a bit like leaving its cozy couch in the middle of winter to hang out outside in the cold in pajamas. Risky and not exactly pleasant.
Contrary to popular belief, earthworms do not have lungs. They breathe through their moist skin, which makes a humid environment—though not saturated with water—ideal for their survival.
Darwin devoted several years to studying earthworms and their ecological impact. He even referred to them as 'natural tillers' for their fundamental role in soil renewal.
Earthworms can detect vibrations caused by nearby rain or predators; they sometimes surface reflexively, which gives the false impression that the rain is pushing them out of the ground.
There are approximately 6,000 different species of earthworms in the world, each adapted to specific environments ranging from forest soils to agricultural land.
Picking up a worm from the surface to place it on overly dry soil can be dangerous for it. Indeed, worms quickly lose their body moisture and require a humid environment to survive. If the soil is too dry, they won’t be able to burrow and are likely to die quickly.
These worms are often caught by heavy rain, which floods their tunnels. In search of air, they make their way to the surface but can quickly find themselves trapped on hard surfaces exposed to the sun or become prey to predators like birds. Therefore, this is not a preference, but an emergency response that can be deadly.
Earthworms play a crucial role in soil health. They contribute to soil aeration, improve water and nutrient exchanges, and create a favorable environment for plant development by recycling organic matter.
Yes, even though earthworms breathe through their moist skin, prolonged immersion deprives them of dissolved oxygen in the water. Therefore, they must remain in a humid but not saturated environment to avoid drowning.
No, they don’t absolutely need direct rain but rather moderately moist soil. Light rain can be beneficial as it helps maintain soil moisture, but heavy rain can force them to emerge from their burrows in a hurry, which is risky for them.
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