morning we followed a path across a wide, dew-covered field. Ahead
us, as far as we could see, the trodden earth was speckled with the
castings of innumerable earthworms. They, in their way, recorded
of vertical migration in the spring.
in the fall, migrate deeper into the earth, below the frostline.
they ball up to reduce moisture loss—as many as a hundred worms
being bunched together—and thus spend the winter in inactivity.
spring comes and frost leaves the soil, the earthworms become migrants
again, tunneling upward. They appear at the surface, leaving the
castings of the new seasons, as soon as the average temperatures of
the ground reaches about 36 degrees.
the same time, the robins return from the South. This is part of
endlessly meshing gears of nature's machine—the appearance of
both earthworm and robins when the thermometer rises to a given point.
over the North, the return of the humble earthworm, the completion
its vertical migration, is a symbol of the arriving spring."
North With the Spring, St. Martin's Press, 1951.