Native worms outnumbered by worldly brethren
Published 4:00 am, Sunday, March 18, 2012
California's native plants have a whole society dedicated to their protection. Native pollinators - bees, butterflies, hummingbirds - have their advocates. Who speaks for the native earthworms?
Your garden worms are most likely exotic - emigres from Europe, a few from Asia. The natives are harder to find. "They're out there, though," said Mission College biologist Thais Winsome, who has studied native earthworms. "Where the habitat hasn't been terribly disturbed, you'll find them."
Winsome's field is not crowded. North American native earthworm specialists could hold conventions in an elevator - passenger, not freight.
Native earthworm science in California began with Gustav Eisen, a Swedish-born naturalist who arrived 1873 for a biological survey and never left. Traveling by mule, he discovered and classified many native earthworm species and is cited in Charles Darwin's "The Formation of Vegetable Mould, Through the Actions of Worms." Most of his specimens were destroyed with the rest of the California Academy of Science's collections in the 1906 earthquake and fire.
One of those 19th century polymaths, Eisen also studied malaria-vector mosquitoes, founded a vineyard in Fresno, introduced avocados and Smyrna figs to California, campaigned to save the giant sequoias, and wrote a multivolume book about the Holy Grail.
There's been little follow-up to his worm work. A 1990-91 Southern California survey turned up several undescribed species; nothing comparable has been done locally.
"No one knows how many species there are in the Bay Area," Winsome told us.
They don't even have common names. Winsome's research at the University of California's Hopland (Mendocino County) field station focused on a beast known only as Argilophilus marmoratus.
It's easy to sort them: "The natives aren't pigmented," she said. "The prettiest ones are white with blue markings, their equivalent of a lymphatic system." In some, the collar-like clitellum becomes coral-red in mating season.
Some exotics, like night crawlers, require constant moisture. Others, originating in Mediterranean Europe, are adapted to our climate: "They either go down about 3 or 4 feet, curl up into a ball and wait out the summer drought, or die and leave egg cocoons in the soil."
These exotics, Winsome said, came in with people arriving at ports with potted plants. "Conditions that keep a plant alive in pots would keep worms alive - even the toughest worm would have trouble surviving a covered-wagon trip."
In human-altered environments, nonnative earthworms have a competitive edge over natives.
"When you find exotics, you're almost always looking at disturbed habitat," she said. "In grasslands, that almost always involves some kind of nutrient subsidy"- fertilizer or cow pies. Farms and gardens, of course, are "disturbed" by definition.
Natives less active
Natives hold their own in undisturbed grassland and oak savanna. Winsome's research suggests that natives are less metabolically active, so don't enrich the soil as much as exotics; that seems to suit plants that evolved in our leaner soils.
Winsome is sure that some local species have gone extinct since Eisen described them. Earthworm conservation is not on the radar of most environmental groups. Readers of Amy Stewart's "The Earth Moved" will recall the giant earthworm of Oregon's Palouse Prairie, 2 feet long and lily-scented. Last year, the U.S. Fish and Wildlife Service rejected a petition to list the Palouse worm as endangered; too little was known about where the worms lived and what threats they faced.
In much of eastern North America, local worm faunas disappeared when glaciers scraped away the topsoil. Exotic worms, beginning with those that reached Jamestown, Va., in the 1600s in a load of ballast, invaded ecosystems free of earthworm-level processes. Their activity has endangered some native plants in the upper Midwest. Out here, the exotics' impact has been less dramatic, and some natives are holding their own.
Winsome hopes to get back into the field someday. "I owe it to all the little things I pickled," she said. "Anything that gets people to think about what's under their feet and the unintended consequences of moving species around is useful."
"The Earth Moved: On the Remarkable Achievements of Earthworms" by Amy Stewart. Algonquin Books of Chapel Hill (confirm), 2004, $12.95.
"The Formation of Vegetable Mould, Through the Actions of Worms" by Charles Darwin. bit.ly/aiHQpx.