May 13, 2012: On this Mother’s Day, I would like to reflect on worms. Is there anything more wholesome and American than earthworms? Mom, apple pie and earthworms! They (the worms ,that is) help churn our gardens up, create soil structure and tilth, deposit organic matter. They are the symbol of Mother Nature and her quiet powerful ways of restoring the earth and natural balance . . . or are they?

I was recently reading an article on an online seminar website for arborists (for short, concise and informative articles on trees and the business of caring for them, I highly recommend ) about earthworms. Though the article did say that earthworms had many benefits for the garden and agricultural land, they weren’t so great for trees and were particularly damaging for forestland. “Heresy!” I cried. Surely this is foreign plot to destroy our faith in these annelid angels, our soil borne buddies. Upon further research, I did indeed discover that foreigners are involved. They are our earthworms! Apart from places in the Southeast and Southwest US, all the earthworms in the northern half of the US and all of Canada are foreign, introduced from Europe or Asia over the hundreds of years of colonization, settlement, agriculture and anglers. All the earthworms that were native to most of North America were exterminated by the glaciers of the Ice Age. Ah man! Another cherished notion shattered by biological truth.

In our vegetable gardens and in agricultural lands, these foreigners are still beneficial, for the reasons I stated before. They have a remarkable capacity to take raw organic matter and convert it to readily useable nutrients in a fairly short period of time. They build soil structure where soil structure is needed – disturbed ecosystems which , no matter how beautiful or serene, your garden is. Those characteristics, however, are not ideal for forestland and by extension the trees in our gardens or streets which are still essentially forest trees placed into non-forest areas.

Here’s the rub. While in your vegetable garden, worms can create better infiltration for the soil, but in the forest it does the opposite. In the forest, it is the forest duff layer, the accumulation of leaves, branches, Forest with duffForest with duffdead chipmunks, etc., that creates a layer that builds the soil and increases infiltration and decreases erosion. It’s a slow process that takes years through the actions primarily of fungi. Worms however can take an entire season of leaves and decompose them in 1 year. Rather than a slow transition, it’s a rapid one and it results in no duff layer. The duff layer is critical to many species of flora and fauna. For many forest wildflowers, such as trillium, trout lilles and mayflowers, it’s the difference that allows them to survive or not. Forest ecosystemsForest withut duffForest withut duff are changed by the presence of earthworms. As duff disappears from the forest floor, then the seeds from larger seeded trees such as oaks are no longer able to hide from predators and disappear. The microfauna such as insects, spiders, amphibians that depend of the cover of the duff are now imperiled also.

For urban/suburban trees in the landscape, research is starting to suggest that earthworms will not cause a visible decline or death, but they do cause water stress in trees – just another stress in the already stressful life of an urban/suburban tree.

The good news is that worms don’t travel much on their own. They can spread about ½ mile/100 years. Less than a snails pace. But as with many exotics, its less about how they will naturally spread than how we will help them spread. Between compassionate anglers dumping their unused nightcrawlers by the side of their favorite forest stream to vermicomposters dumping worm compost on their newly planted trees the foreign invader is aided and abetted by us. As Pogo would say, “We have met the enemy and he is us.”
At least one state, Minnesota, has recognized the foreign peril and has a state statue making it illegal to dump worms in the wild. They even have their own worm homeland defense webpage, What can you do to stem the tide of these slimy invaders?

- Dispose of worm bait in the trash not the woods.

- If you must use vermicompost on trees, freeze it solid first.

If I have been unduly harsh on earthworms, it’s because I’m feeling a little betrayed, like when I found out last year that Santa Claus was really my parents. Worms are good in the vegetable garden or flower beds or the crop field – disturbed environments (or at least until new research proves otherwise), but they’re not around trees. I think what disturbs me also is that the natural world is not very simple. When you think you’ve got a handle on it, you probably haven’t. No saints or sinners in the natural world, just things doing their thing.

There’s still Mom and apple pie left. . . . but is apple pie a native or an exotic? . . . I don’t want to go there today.

F & P