Migrating Earthworms
A Vertical Migration

In his book North With the Spring, naturalist Edwin Way Teale describes the "vertical migration" earthworms undergo each fall and spring.

"One morning we followed a path across a wide, dew-covered field. Ahead of us, as far as we could see, the trodden earth was speckled with the castings of innumerable earthworms. They, in their way, recorded a form of vertical migration in the spring.

"Earthworms, in the fall, migrate deeper into the earth, below the frostline. Sometimes they ball up to reduce moisture loss—as many as a hundred worms being bunched together—and thus spend the winter in inactivity.

"When spring comes and frost leaves the soil, the earthworms become migrants again, tunneling upward. They appear at the surface, leaving the first castings of the new seasons, as soon as the average temperatures of the ground reaches about 36 degrees.

"At the same time, the robins return from the South. This is part of the endlessly meshing gears of nature's machine—the appearance of both earthworm and robins when the thermometer rises to a given point. All over the North, the return of the humble earthworm, the completion of its vertical migration, is a symbol of the arriving spring."

From: North With the Spring, St. Martin's Press, 1951.

Journal or Discussion Questions:

  • What do robins eat when worms are not available?
  • Why do you think it would make sense for robins to migrate with the 36 degree isotherm?

Try This! Graph the Soil Temps

  • When the first earthworms emerge in your area, take temperature readings of the soil in places where you see worms, and in places where you don't. Try to get a reading right at the soil's surface, and at depths of 3, 6, and 12 inches. Graph your findings and compare. What do the graphs tell you?