Why are there so many earthworms after the rain and so few at ordinary times?

Earthworms move in the soil on weekdays, and you can't see them, so you think they are few.

Once it rains, the cracks in the soil are full of rain, causing earthworms to "breathe" on the ground without air to breathe.

Of course, earthworms have no lungs, and they breathe by air infiltrating into moist skin. The ground is relatively dry, and the skin is easy to dry, which will lead to their poor breathing, while the soil is relatively humid, so it is not easy to see earthworms in rainy and dry weather.