We had 3-4 months of rain this summer, here in Missouri. You would see many worms come up to travel around the top of the soil. You would also see many birds feasting on them. Temperatures were cooler than normal too. (70f/21c+/-) But, still in the range for worms to be happy.
the fall and spring. There were may giant night crawlers to be found. Earthworms like cool temperatures of 50 - 70 degrees F (10-21C) and
moist conditions. Earthworms aren't active
when it's cold or dry. So that is the answer. They are hiding out deep in the soil. Waiting for the right conditions. We have not had much rain since early August.
I was starting to think the worms may have drown or floated away. It is possible. But I have read can survive for several weeks under
water providing there is sufficient oxygen in the water to support them.
They will come to the surface of the ground as a response to high relative humidity. They can move around safely without drying out thanks to the humid condition.
They breathe through their skin, yet the skin must stay
wet in order for the oxygen to pass through it.
Earthworms will dye if they are frozen, so the go deep below the frost line till the ground thaws.
live deep in the soil, where smaller worms live near the surface.