The good, the bad, and the ugly of earthworms

Help! I noticed hundreds, maybe thousands of invading alien creatures crawling through my soil when I was planting my garlic crop a couple of weeks ago.

But hold on to your shovel. As scary as it sounds, the animals writhing around in my vegetable plot are not from a horror movie marquee, nor some terrifying creature that will send panicked citizens screaming through the streets.

These aliens are common earthworms that we all find when digging in the garden – the same ones collected at the local golf course by those nocturnal guys with headlamps and buckets strapped to their legs to be sold as bait to fishermen hoping to bag the big one.

The wrigglers give us a warm fuzzy feeling when we find them doing their work in the compost heap, then rack us with guilt when we accidentally divide them in two with the shovel. And if my fading childhood memories serve me correctly, worms make pretty good eatin’ when you are a curious five year-old playing in Grandma’s backyard flower garden.

So what’s all the fuss and why are these benevolent little soil processing machines considered alien invasive creatures?

Well, it’s because every native earthworm that existed in Ontario before the last ice age was completely eliminated during the period of glacial recession and virtually every garden variety worm living in our soil today is a foreign species that was introduced only a few hundred years ago by human activity. All of them are descendants of worms that managed to hitch a ride across the Atlantic during European settlement and arrived here in soil used as ship ballast or muddy root-balls of imported plant material.

Of course, every gardener and farmer I have talked to have nothing but good things to say when they find a healthy population of these little creatures in their soil. The worms’ colossal appetite allows them to constantly vacuum their way through mounds of decaying organic matter and deposit their weight in nutrient rich castings back into the soil every 24 hours. Along the way, they aerate the soil with endless burrowing and distribute minerals and essential elements deep into the root zone of established plants. They also provide an abundant source of food for birds and wildlife when they happen to crawl to the surface after a rainstorm.

But with the good, there is also a bad and an ugly side of worms. When they make their way to virgin forests the negative effect has been severe enough for the Ministry of Natural Resources to issue a warning against the transport and disposal of these non-native invasive species into naturalized forested areas. The main culprits are land developers who move soil to forest borders and surprisingly, fishermen who discard their unused tubs of bait in lakeside woodlands with the misguided belief that they are contributing to a healthy ecosystem.

The concerns naturalists have with introducing earthworms to our forests stem from the fact that Ontario’s woodland areas evolved quite nicely without them. The secondary native plants and animals that emerged within this ecosystem continue to depend heavily on a thick layer of worm-free leaf litter called ‘duff’ for seedling germination and protection from the elements.

Lately, biologists have noticed that when large populations of hungry earthworms are present in forests a substantial amount of this duff disappears. One species, the European dew worm (a favourite bait for anglers) is a large and voracious surface feeder that reproduces rapidly and can chomp its way through large swaths of leaf litter during its nighttime feeding activities, eventually leaving significant amounts of the forest floor with bare soil and a condensed layer of castings that plants and seedlings can’t penetrate.

Unfortunately, these dramatic changes may soon reach the point where some of our more delicate native plants and animals could become critically endangered species.

A native orchid called Small Whorled Pogonia (Isotria medeoloides) has already reached endangered status because of the lack of leaf cover and fungi the plant depends on to survive. This loss of habitat and the open bare soil left behind by earthworm activity has also opened the door for foreign invaders like garlic mustard and dog-strangling vine to move in, both of which are notorious for overpowering other native plants such as trilliums and ferns.

So there it is, the good and the bad side of our friendly little earthworms. As for the ugly side … I’ll leave that up to your imagination.

 

Steven Chadwick is a professional gardener and horticulturist, and long-time Beach resident

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