Earthworms often come to the surface when it rains, and there are a few main reasons scientists think this happens:
Breathing & Oxygen
Earthworms breathe through their skin, which must stay moist to allow oxygen to pass through. Soil pores can flood during rain, reducing available oxygen. Coming up to the surface helps them avoid suffocating in waterlogged soil.
Easier Movement
Wet ground is softer and slicker, making it easier for worms to travel across the surface. This helps them spread out to find food, mates, or new territory.
Avoiding Predators Underground
Prolonged water saturation can bring other soil-dwelling predators (like beetle larvae) closer to them. Surfacing might reduce that risk—at least temporarily.
Mating & Reproduction
Some researchers think rain provides a safe, humid window for earthworms to come out and reproduce without drying out.
Confusion Factor
Vibrations from raindrops can mimic the vibrations predators (like moles) make when moving through the soil. This may “trick” worms into surfacing as an escape response.
So it’s not just about “escaping drowning”—earthworms can actually survive underwater for days if the water is oxygen-rich. It’s more about oxygen, mobility, and survival strategies.