When it rains, we are likely to have a different smell in the air, wet socks, and to cross paths with an earthworm or two.
Although it used to be considered that worms would simply drown in the rain, it would appear that there are a few potential reasons as to why our ground-dwelling friends actually want to join us in the deluge.
Theories and research state that worms may come out when it rains for the following reasons:
- They may drown if their underground environment is submerged in water (though it can take days for worms to drown)
- Vibrations from the rain making them think a predator is about to invade their home
- Easier for earthworms to move across wet surfaces
- To find a potential mate in a more moist environment and reproduce
We discuss these reasons in more detail as to why worms come out when it rains – and how to stop them popping up if you need to…
Do worms drown in the rain?
As you will have noticed, you are far more likely to notice worms when it’s raining on the soil’s surface.
It would appear that with just a simple change in the weather, worms emerge on the street, on the soil surface, on the driveway, etc. So why do worms appear on the soil’s surface whenever it rains?
Soil experts once believed that the earthworm species made its way out of the soil when it rains due to the high risk of drowning beneath the surface.
As you may know, earthworms breathe through their skin. This is why they require moisture in their environment in order to survive.
However, too much moisture can be a bad thing. One theory was that the excess of water from a rainstorm could potentially drown the worms, leading them to surface in search of more oxygen.
On the other hand, new research has shown that worms can, in fact, spend several days fully submerged in water without drowning.
They do not, in fact, appear to react to water in the same way that we humans do, meaning that whenever they surface to the top of the ground, it’s for other reasons.
Why do worms come out of the ground?
Instead of the rain affecting the worms’ moisture requirements, scientists have found that it is less to do with the effect of the water and more due to the rain vibrations that so many worms come to the surface when it rains.
Indeed, the vibrations created by the hard rain remind worms of predator vibrations (such as from moles).
As you can imagine, their natural instinct kicks in, telling them to leave their burrows as quickly as possible, thus regaining an area where few earth predators go, especially in the daylight, the surface of the ground.
Another theory is that worms find it easier to travel greater distances on wet soil.
As worms do not have lungs but instead breathe through their skin, this skin is indeed very sensitive, meaning that a dry environment will not help them to feed or even to move.
The wet surface will hopefully, for them, stay moist for as long as possible to help them gain the distance over the terrain that they are searching for.
Finally, it is also believed that it is far easier for certain worm species to find a mate than it would be on dry land due to the moist environment.
However, you may have noticed many worms join the ground surface even when it isn’t raining. Scientists have found that this is in part due to birds.
It would appear that these clever creatures have figured out that worms and other insects will climb to the surface out of fear of ground predators, such as moles.
Whether they know who the other culprits are is neither here nor there; what really matters is that they have learned to recreate those specific vibrations in a similar way, to encourage the worms to leave the soil, and join the surface.
It is an incredibly intelligent way of hunting for their food, as birds do eat worms.
How Do You Prevent Rain Worms?
Although earthworms are incredibly beneficial to grass, plants, and general life on earth (as they aerate the soil, make it easier for plant roots to get their nutrients, consume decaying organic matter to produce castings for compost), not everyone enjoys seeing them flood the surface when it rains.
Too many earthworms all in one place can indeed be damaging to an area, more so than good.
However, you should never use chemical pesticides to control the worms.
For example, it is essential for anyone in waste and environmental management to know that harsh chemicals will damage the soil and most of its inhabitants.
Moreover, there is no specific earthworm pesticide that will attack them alone, meaning general chemicals will cause widespread harm.
Instead, you should try using a more natural way of controlling the vast majority of earthworms that could surface in an area where you do not wish to see them.
You could try planting soil fabric a few centimeters below the surface, preventing the worms from breaking through onto the surface.
You can also try putting out some mustard powder over your soil. The powder is too hot for a worm and will irritate them, thus sending them into another direction to escape the heat.