The Worms Crawl In, The Worms Crawl Out....

It seems like I'm seeing worm castings everywhere I go these days, like these I photographed this morning on the trail in the Back Five.

The castings started appearing earlier in the year than I expected - I started seeing them weeks ago - and they are more granular than I thought they should be.  In fact, at first I wondered if these little piles of dirt were actually worm castings at all.

I've recently been reading Life in the Soil:  A Guide for Naturalists and Gardeners, by James B. Nardi, and I found the section on worms fascinating.  Did you realize that the earthworms we see in our gardens are not native to North America but were brought here from "The Old World"?  There are native earthworms, but these are smaller and exist mainly where there is undisturbed native vegetation.    The native earthworms work at a more "measured pace" than introduced earthworms, a pace that better matches the actual accumulation of detritus in North American forests.  Because of this difference in the activity levels of native compared to introduced species, introduced earthworms have been found to be actually depleting the leaf litter (and thus the animals and plants associated with it) in many of the North America's forests.

According to Life in the Soil, identifying different earthworm species involves characteristics such as the number of segments between the clitellum and the head of the earthworm, the number of segments the clitellum takes up, and the shape of the first head segment.  No, I haven't attempted this yet!  (But I probably will, if I can find a decent guide....)

Earthworms will dig as deep as 10 feet, and they literally eat the soil as they push their way through it.  The resulting manure - the earthworm's castings - is both less acidic and richer than the soil the earthworm took in.  Calcium carbonate has been secreted into the material by glands along the earthworm's gut, and the resultant castings therefore have about 50% more available nitrogen, phosphorous, potassium and calcium than the surrounding soil.

Earthworms move a surprising amount of soil.  Nardi reports that Darwin's last book was about earthworms, and that Darwin estimated that earthworms produced about 40 tons of castings/acre/year on the soil surface in Britain.  He also estimated that this activity would cause objects to be buried at a rate of 0.1"/year simply by the actions of earthworms!

I guess the earth really is moving under our feet when there are plenty of earthworms in it!