Do you have webworms in your gardens?

·3 min read
Although they may look gross and off-putting, the webworms are an important food source for birds.  (Ishita Verma/CBC - image credit)
Although they may look gross and off-putting, the webworms are an important food source for birds. (Ishita Verma/CBC - image credit)

With summer ending, it seems even trees are getting in the spooky spirit, with cloth-like netting covering their leaves and branches.

But those webs aren't from spiders. Fall webworms are moth caterpillars that are native to North America.

Webworms can typically be seen later in the summer, munching on a whole variety of deciduous trees such as maple, elm and poplar. For the most part, they aren't picky bugs.

Unlike other caterpillars, webworms like to live in large communities.

After hatching the larvae, they will stay together in a community to build a large web nest to use as shelter.

"It protects them from things like birds and ants and other predators that might affect them," said entomologist Ilan Domnich.


Because the nest is so tightly wound, the temperature inside them is high, which increases the metabolism of the worms and speeds up their development.

The webworm will go through six different stages as a caterpillar, staying close to the tent and only venturing out to eat.

"That's when people will notice defoliation in the trees, when those big caterpillars are eating lots of leaves," Domnich said.

Do webworms cause damage to the trees?

Webworms don't always damage the trees.

If you get a normal webworm population, they may eat all the leaves off of a tree, Domnich said.

"The tree won't be very happy, but it'll be just fine. Next year, it will grow all new leaves," he said.

However, if the webworm population comes back year after year, trees could get stressed out and eventually die.

"But that will typically only happen when you get these huge outbreak populations," Domnich said.

The worms go through cycles, where there's just a few of them around and next year they're everywhere.

How can you treat webworms?

One way to treat webworms is by using pesticide, one that specifically targets caterpillars so as to reduce harm to other types of insects.

"All the other bugs, everything that's eating the bugs, the birds and everything like that, it's all part of the same ecosystem," Domnich said.

Following the rules and guidelines for pesticide spraying is very important, Domnich said.

"You never spray when it's going to rain because it's just going to wash out," he said.

Similarly, you never spray during the middle of the day when pollinators are active.

Another way to control the caterpillars, Domnich said, is to simply pick them up and throw them away.

Ishita Verma/CBC
Ishita Verma/CBC

"The best way to get rid of them is just to use ... a garden fork, or those forks you use for roasting hot dogs and just reach up into the web and twirl it like you're picking up spaghetti, and just pull the web out of the the tree," Mike Jenkins, pest management coordinator for the City of Edmonton, told CBC's Radio Active.

Webworms don't have itchy hairs and they also don't bite, making them safe to grab.

"Or remove the cocoons, if you see those," Domnich said.

The cocoons are spun out of silk and look like a big fuzzy pill, about an inch long.

Once in the cocoon, the caterpillars fall to the ground, pupate over the winter and hatch out as moths in the spring.

While the image of worms in a web nest can be gross and slightly off-putting, webworms are a great food source for birds, and are an important part of the ecosystem, Domnich said.