Worm Wars: Charlotte's cankerworms are nearly gone, but tree bands are still going up
If you're new to Charlotte, let's catch you up on an unusual holiday tradition that takes place around this time of year, but seems to be declining.
It's called cankerworm banding. Every year around Thanksgiving, many of us buy rolls of plastic and insulation, wrap them around tree trunks, then coat the plastic with sticky, resiny-smelling goop.
Charlotte City Arborist Laurie Reid Dukes got an early start this past week on a tree in Elmwood Cemetery in uptown.
The tree sat on a hill surrounded by old tombstones. Dukes walked slowly around the trunk, spreading the goop with a small paint spatula.
"It kind of reminds me of like, caramel ice cream topping," she said, noting the goop's brown color.
Why do we do this? For years, these sticky tree bands have been the main weapon in Charlotte's ongoing war against the little green cankerworm.
The little worms have buried themselves in the ground, and in the next few weeks after a big frost, they'll emerge as moths.
The males have wings and fly. The females are wingless and will crawl up the sides of a tree to lay their eggs in the branches, so their worm babies can hatch in the spring and gobble up the tree's baby leaves.
Unless they're stopped by this sticky goop.
"The main point is to catch the female moths as she's coming up out of the ground so she can't lay her eggs," Dukes said.
The worm population plummeted in 2017 and 2018
These tree bands used to be everywhere in Charlotte because — for many years, the worm population was out of control, with baby worms chomping through the tree canopy and flying in people's faces on silken threads.
But that's changed. Over the past five years, the number of adult moths counted on tree bands by city workers has plummeted from 35,000 to 40,000 in 2015 and 2016 to just 121 last year.
That means a lot of people aren't banding their trees anymore. Even the city has pulled back from banding about 5,000 trees during the height of the worm infestation to now just 500.
Dukes said the sticky bands helped cut down the worm population, and for a few years, the city dumped insecticide from planes and helicopters over the tree canopy, killing many worms. But Dukes said what really did it may have been the weather.
"In 2017 and 2018, we had really really cold, cold nights," she said. "So about that time of year, usually in March as the leaves have just started coming out, the little tiny caterpillars hatch out ... So if we have several nights of below freezing temperatures, I could definitely see how that's going to impact the caterpillars or the leaves — the food material. I really, honestly think that's what brought our numbers down so low."
She said it could be interesting to see if this impacted local birds that depended on cankerworms for food. No studies have been done.
It might also be interesting to see if the worms that survived have evolutionary traits they might pass on to their offspring.
The cankerworms could still return
Before we roll out the "Mission Accomplished" banner and declare victory, Dukes cautioned that the little guys could make a comeback.
"It always has that risk to be able to build back up again. We have the trees. We have the food source," she said.
That's why the city will still band 500 trees this year, just to keep an eye on things and prevent a possible Worm War II.
Dukes said private citizens can likely skip tree banding this year, unless they saw cankerworms in their trees in the spring, in which case tree banding is still a good idea.
If you do band your trees, the city has a citizen science project where you can count and report cankerworms — kind of like a worm informant.
Still, the tradition will live on with the 500 trees banded by the city over the next few weeks, starting with this very first one in Elmwood Cemetery.
As Dukes finished spreading the goop, she stepped back, removed her gloves, and smiled.
"That's it! We're banded" she said.
And now the holidays have officially begun, at least for this city arborist.