I was recently asked why there were so many earthworms on the sidewalk lately. I should add that it has been raining almost non-stop for about three months and we are more than a foot over the annual rainfall average.
I thought I came up with a very likely explanation. I answered that the worms may be forced from the ground due to it being saturated with water keeping them from being able to breathe. Sounds like a great reason and it was except for one thing. It was not correct.
A little research quickly revealed that the worms come out of the ground after heavy Spring rainfall in an attempt to migrate. The moisture on the ground and sidewalk allow them to have the ability to migrate faster and farther than they could underground. Apparently they have a built in dispersal "need".