Worms undermining the future of forests

By For The Columbus Dispatch  • 

The dumping by fishermen of unused worms onto the ground near shore or bank is apt to strike most people as not only sporting to the worm but as beneficial to the soil.

Karma would suggest that, provided it’s not too dehydrated and torpid to become anything but wild animal food or a sun-baked mummy, a worm spared impalement deserves a shot at crawling back into the happy home turf from whence it came.

Aye, there’s the rub.

Worms sold to anglers, including the ubiquitous 6- to 9-inch lumbricus terrestris, aka nightcrawler, in reality are interlopers on the Ohio loams. Nightcrawlers, in fact, are an invasive native of Eurasia brought by European settlers to North America as stowaways in ship ballast and hitchhikers in potted soil.

Glaciated Ohio, along with the rest of ice-covered North America, held no earthworms of any kind when the Shawnees, Wyandots, Delawares, Eries and other native peoples followed the forests that began to grow up about 10,000 years ago, after ice sheets retreated north.

With neither earthworms nor, for that matter, empty soup cans to hold them, what did those indigenous anglers use to bait their hooks of bone?

True enough that big fish eat little fish, which begins to answer the question. And, too, big fish eat little frogs. Also caterpillars, cicadas, hellgrammites and crawdads were among the natural bounty from which the earliest anglers could select as piscatorial enticements.

On the other hand, predator fish of all sorts and sizes seem to find the newcomer worms as desirable as anything they’d eaten before. Did Great Lakes fish develop a taste for worms over time, or did they take to them from the start like Europeans took to tobacco?

In both cases so delightful, yet so lethal.

The fact that earthworms have proved to be a boon to robins, walleyes, moles, gardeners, compost makers and purveyors of bait doesn’t alter history. The fact that non-native earthworms seem to be causing problems in North America’s forests could change history.

Though little has been made of the situation in Ohio, where the climax forests were mowed down practically to nothing starting a couple of centuries ago, a few Great Lakes states with significant tracts of primordial trees are trying to fend off worms.

Minnesota, for instance, makes it illegal to dump exotic species into the wild, leading the Great Lakes Worm Watch — an educational agency affiliated with the University of Minnesota Duluth — to hint that anglers risk a fine if caught releasing exotic worms into the woods.

Worm Watch suggests that fishermen should not only “dispose of unwanted bait in the trash” but ought to be spreading “the dirt” about the worm threat.

North America is home to about 100 species of native worms, but none of them lived in glaciated territory, which includes much of the land that comprises the Great Lakes states. Consequently, hardwood forests developed around lakes in soil that held no worms.

Without worms, the forest floor develops a spongy layer of organic “duff.” This layer is the natural growing environment for native woodland wildflowers, provides habitat for ground-dwelling animals and helps prevent soil erosion, a Worm Watch paper states.

Research has shown that the presence of earthworms, which feed on decaying leaves and related duff, actually compacts forest soils. The result is that the understory plants, such as wildflowers, ferns and young trees, have a hard time getting a foothold. When older and established trees die, their replacements are few and sometimes insufficient.

Photographic evidence of what has already taken place in some spots can be seen at the web site greatlakeswormwatch.org.

Ohio’s important sugar maple trees, particularly in northeast Ohio, are in places being stressed by soil alterations wrought by earthworms.

That humans have been spreading a problem became obvious only in recent years.

The worms expand their range oh-so slowly on their own — less than a half-mile in 100 years, a Worm Watch fact sheet states. Native southern worms are believed to have moved only about 30 miles north in the 100 or so centuries since the glaciers departed, research suggests.

That puts humans as the primary vector in the spread of non-native earthworms. About 15 species of invasive worms have been identified, and not one got here by swimming the Atlantic. Not one can much expand its present range without a helping human hand, often enough the hand of a fisherman.