Gardening Articles: Care :: Pests & Problems

Planarians invade

by Veronica Fowler

What gardener doesn't love earthworms? They're among the best soil builders, transforming organic matter such as autumn leaves into humus and nutrient-rich soil. They're also powerful miniplows. In one year, worms on 1 acre of healthy soil can work through about 50 tons of soil, improving its texture while contributing about 5 tons of nutrient-rich castings.

So earthworm lovers are especially nervous about the possible encroachment of earthworm-eating planarians. Planarians are definitely yucky creatures. They measure 2 to 6 inches long, are slim and flat, and often have stripes running the length of the body. And they leave a slime trail similar to that of slugs. Tropical species of planarians such as Bipalium kewense (also called the hammerhead worm for its broad head) and Dolichoplana striata (which has a long, tapering head and subtle stripes along the body) have been in Florida soils for years. These species are not known to cause severe damage to natural earthworm populations, although commercial earthworm growers occasionally suffer severe losses.

Of greater concern are the temperate species of planarians, such as Geoplana sanguinea and Artioposthia triangulata, from New Zealand, which have been gobbling up earthworms in Britain and Ireland. In some areas, earthworm populations have been cut in half.

In this country, recent research in New York has revealed that at least one temperate species, Bipalium adventitium, is widely present. --In all the suburban areas we've checked throughout the state, we have found these flatworms in the soil,-- says Pete Ducey, biologist at the State University of New York in Cortland. The implications for native earthworm populations are unclear. --It seems these flatworms have been around the Northeast for years, but there has been little study of them to determine what impact they have on earthworm populations,-- Ducey says. In lab tests, B. adventitium is slow to reproduce and eats only two earthworms a week. However, if many planarians are in the soil, they can adversely affect earthworm populations.

B. adventitium is 1 to 3 inches long, tan-colored with a single dark stripe on its back. The head is half-moon shaped, the body flat and narrow. The body is narrower than a slug--s and slimy.

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