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<\/p>\nHundreds of thousands of caterpillars \u2014 maybe millions \u2014 all of them hungry for poplar leaves. Numerous forest tent caterpillars are worming their way around Edmonton branches.<\/p>\n
Creepy, but essentially harmless and native to the Alberta ecosystem, they are helpful for the forest, over all, although trees already suffering poor health may not fare as well.<\/p>\n
The writhing critters can, however, turn a bike path into a hazard, cautions Mike Jenkins, senior scientist for the City of Edmonton.<\/p>\n
Rising numbers year after year suggest the Malacosoma disstria is on a 10- to 15-year roll in Edmonton.<\/p>\n
\u201cThey\u2019ve emerged from their egg cases and they\u2019re moving out on to the leaves of the poplar trees and growing from there and they kind of start off in little clusters. You\u2019ll see a big patch of them sitting on the trunk of the tree all together,\u201d Jenkins told Postmedia.<\/p>\n
<\/p>\n
Forest tent caterpillars in the Edmonton river valley on Friday, June 5, 2026. Forest tent caterpillars are native to the Edmonton area and have a distinct row of whitish spots running down their backs and wide blue bands along their sides. Shaughn Butts\/Postmedia<\/p>\n
When the fuzzies get big enough, unlike their cousins, the Eastern tent caterpillars, they don\u2019t actually make tents in trees.<\/p>\n
Instead, they look for a spot to cocoon \u2014 other trees, your fence, your garage. Your house.<\/p>\n
\u201cThey spin themselves sort of a little silken pierogi and pupate inside there for about a week or so,\u201d Jenkins said.<\/p>\n
A week later, a little chunky brown moth comes out around the end of June \u2014 and where there are bright lights in the big city, big clouds of them fly around. And mate. Many become crispy protein snacks for birds, bats, reptiles and amphibians and small mammals.<\/p>\n
Many will lay a band of eggs on the tips of poplar branches, little rings of tiny black \u201cbeads\u201d that winter on the branch tips, hatching out into a new batch of caterpillars in the spring.<\/p>\n
When the numbers boom too high, natural enemies take advantage and help control the population. Ground beetles, normally ground foragers, forego slugs, grubs and cutworms, going Tarzan to climb trees with a yen for caterpillars.<\/p>\n
Ants, parasitic flies and wasps, oh my \u2014 caterpillars are their jam.<\/p>\n
\u201cThere are birds that actually expand their range to take advantage of some of those outbreaks \u2014 red-eyed vireos we don\u2019t usually see in very large numbers around here, but when there\u2019s an outbreak of forest tent caterpillar, they end up moving in to take advantage of that food source,\u201d Jenkins said.<\/p>\n
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<\/p>\n
Forest tent caterpillars in the Edmonton river valley on Friday, June 5, 2026. Shaughn Butts\/Postmedia<\/p>\n
Then there\u2019s viruses. Nuclear polyhedrosis is something of a body-snatcher, turning their insides into liquid, leaving them dangling dead from the tree by their forelegs.<\/p>\n
\u201cThen if anything touches them, they kind of burst open and spray virus-laden goo all over all the rest of the caterpillars and spread the virus that way,\u201d Jenkins said.<\/p>\n
If it all sounds too Aliens vs. Predator, don\u2019t worry \u2014 it\u2019s nature balancing things out.<\/p>\n
\u201cIt helps to get a bunch of the nutrients that are in the trees basically into the soil as the caterpillars turn it into caterpillar frass.\u201d<\/p>\n
(That\u2019s science for caterpillar poop.)<\/p>\n
\u201cFrass is a good nutrition for lots of the other things that are in the forest,\u201d he said.<\/p>\n
Edmontonians have nothing to fear but the fear of bugs itself. The poplar trees have evolved to bear getting stripped several years in a row, although trees that are already in poor health may be worse for wear.<\/p>\n
\u201c(Poplars) can actually photosynthesize a little bit, even with no leaves at all. They\u2019ve got chlorophyll underneath their bark, and it\u2019s probably part of their adaptations for being regularly stripped by caterpillars like this. The trees will survive,\u201d Jenkins said.<\/p>\n
And if the sight of hundreds of caterpillars writhing on your home\u2019s exterior is disturbing, just think, they can actually become a road hazard when they\u2019re crossing a street or a roadway. Ontario\u2019s tent caterpillar outbreaks have been severe enough to cause accidents.<\/p>\n
Jenkins hasn\u2019t seen caterpillar slicks for a long time, but in the \u201980s, bike paths got treacherous with them, he said.<\/p>\n
So what does it sound like?<\/p>\n
\u201cThere\u2019s a pretty distinctive popping sound, and yeah, definitely you can lose traction fairly quickly,\u201d he said.<\/p>\n
As a science-minded kid, Jenkins learned about caterpillars the hard way \u2014 there was the jacket that went through the wash with a couple dozen caterpillars in the pocket, and then the beer case of caterpillars left in the living room, forgotten, when the kids were called for dinner.<\/p>\n
\u201cBy the time dinner was done, there were caterpillars all over the living room. We tried to argue for a stay of execution, but they did not grant one,\u201d he recalled.<\/p>\n
Related<\/p>\n
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