Like most Americans, according to numerous polls, WGBH listener Stefanie Covino is concerned about climate change. And she’s found herself increasingly curious about what it means, in particular, for one of our fellow creatures at the bottom of the food chain. She recently to reached out to WGBH’s Curiosity Desk for some guidance:
"I'm wondering: What do you do with worms when they get washed onto sidewalks and streets? Do you put them back in the grass? Do you leave them alone? Especially since it's raining a lot more and there's a lot of impervious surfaces that are changing how that water runs off and where the worms end up. What is the right thing to do?"
Humans have been altering the landscape for as long as there have been humans, so where to begin? Let’s take 1620, and the arrival of full-time European settlers in New England. There was plenty of wild forest, and — to Stefanie’s point — no paved roads or sidewalks. There were also no earthworms.
"Most of the worms we have here in New England are exotic worms, which means they are from somewhere else," explained Josef Gorres, an associate professor of soil ecology at the University of Vermont.
When the glaciers retreated at the end of the last Ice Age around 15,000 years ago, they left the soil below New England essentially wormless. The worms so common here today were pilgrims too, hopping rides from Europe, and later Asia, in plants and food stuffs brought in tow across the ocean.
"Some of them are highly invasive," said Gorres. "Which means they reproduce very fast, they can feed really fast on resources, they are able to adapt to new environments."
This includes the lumbricus terrestris, a.k.a. the common nightcrawler, and a bunch of its cousins — essentially all those reddish-grayish-brownish worms we all picture when we think of an earthworm. The term "invasive species" sounds pretty bad, and yet conventional wisdom suggests these guys are good for the soil. So, what gives?
"Worm health is indicating soil health," said Jim Cole, barn manager at a Mahoney’s Garden Center in Boston. "No matter what soil. Whether it’s flowers, veggies, lawn — the more there are, the better it is."
Indeed, he says, these non-natives should be considered honored guests in places like city parks, backyards and home gardens.
"So, they help with water filtration, they help recycle organic material, they stimulate other beneficial living organisms," said Cole.
But it’s a different story in the forest.
"What is usually in a typically hardwood forest in New England is a pretty thick layer of organic material," said UVM professor Gorres. "It’s loose but it’s firm."
Gorres says this crucial layer on the forest floor protects seeds so they can germinate, promotes fungi growth, and staves off erosion after rainfall. But when you get too many worms burrowing under and through it, and munching on all that loose material, it collapses. This can prevent some plants from setting root and expose seeds to predators like birds and chipmunks.
"And the upshot of that is that in the end, there are fewer plants there," said Gorres. "There is less biodiversity."
Destruction of the forest floor due to invasive worms hasn’t been a huge problem in Massachusetts, according to the Department of Conservation and Recreation (DCR). After all, most of the worms have been around for hundreds of years now. But there is a new kid on the block: the so-called Asian crazy worm.
To the naked eye, the Asian crazy worm — or jumping worm — which entered the U.S. in recent years, looks a lot like a nightcrawler. But unlike those languid crawlers, if you pick up an Asian variety, it will slither and jump wildly — hence the name.
"Those are not good," said Ken Gooch, the forest health program manager for DCR. "They are an issue now. They are heavy, heavy feeders. [They] eat all the organic material and basically leave the soil without nutrients."
Gooch says these Asian worms have wreaked serious havoc in other parts of the U.S., like the upper Midwest. And that has him and his team paying attention.
"There is evidence of it in New England," he said. "Here in Massachusetts, in Maine, in New Hampshire. But I think it’s very limited right now."
And the DCR wants to keep it limited. These guys aren’t just bad for the forest, they are also just as bad for your lawn or garden.
With all this in mind, to answer Stefanie's question: If you see a worm on the sidewalk, first make sure it’s not an Asian crazy worm. If it is, maybe don’t move it. And also, alert the DCR or the Department of Agriculture. They want to know.
Beyond that, Gorres says, it’s really up to you.
"If there’s one on the ground, that means there’s probably millions in the grass," he said "I think what you should do is you should go with your conscience. So if she feels bad about that worm, by all means, put it back in the grass. Just don’t put them in a forest that doesn’t seem to have any earthworms."
