Tuesday, July 10, 2007

Earthworm Revelations


"It is both fascinating and a little disturbing to pull something out of the ground and stare at it, something that does not belong up here with the rest of us." --Amy Stewart, "The Earth Moved: On the Remarkable Achievements of Earthworms"

I found out a lot about the earthworms in my garden after reading Amy Stewart's book. For one thing, my worms were not bathing in the moonlight when I observed them half out of the ground. They were most likely foraging and dragging organic materials into their burrows. That's assuming the worms I saw in my garden at night were the same earthworms Charles Darwin studied, Lumbricus terrestris (nightcrawler), which do leave their burrows at night (other worms don't seem to feel the desire to wander about on the surface).

One thing Darwin discovered in his study of worms was that earthworms have enough intelligence to determine which end of a dead leaf will fit most easily into its burrow. Before him, no one had really observed the activities of earthworms. But Darwin did more than observe: he conducted experiments with little triangles of paper to see which end--the narrow end or the wide end--the earthworms would grab. Out of 303 little paper trianges, according to Stewart, the earthworms grabbed the narrower end 62 percent of the time. Darwin concluded: "We may therefore infer--improbable as is the inference--that worms are able by some means to judge which is the best end by which to draw triangles of paper into their burrows." Oh, and although they are sensitive to light, earthworms are blind. So how do they do that?

I have seen a few really large nightcrawlers--like 8-10 inches--in our garden before, but the ones I have seen most recently are shorter. Those long ones make me shudder, only right afterward I say "Nice worm!" to recondition myself. I know worms are good for the soil, at least soil that I want to grow things in, but those really long ones are, well, disturbing. When I'm digging to plant things, I see other worms: smaller, thinner, pinkish or even grayish. They could be Lumbricus rubellus (redworm) or Aporrectodea turgida or Aporrectodea tuberculata or Allolobophora caliginosa (gray worm or field worm), names almost as long as the worms themselves. These are all common garden worms, non-native to the U.S. and spread by European settlers. There are a few native California worms but they do not live where the soil has been disturbed by humans, unlike the non-native species.

I would like to know just what is on the end of my trowel, but it's surprisingly hard to find out. So far I can't find anything online that lists which worm species are common to San Francisco, or even the Bay Area, specifically. There is Worm Watch, a Canadian site with a detailed field guide for identifying one's own worms (and reporting one's findings to the Canadian government in the interest of monitoring the distribution of worm species), so if we have some of the same species, I suppose I could try identifying them myself. I called the SF Garden for the Environment, and the staff person knew what species of worms were in the worm composting bins, but not the ones living in the soil. She said if I find out, please call her back to let her know.

The photo is from kidcyber.com.au, species not identified.

1 comment:

Joyanna said...

Wow, this is great, Daphne! I'm so glad you posted this! The world can't know enough about worms, as far as I'm concerned-- you've inspired me to check out the nearby UM biology department for worm species in my region. Thank you!