Caterpillars Taking Over Alberta This Spring
Alberta residents are dealing with an unusually high number of forest tent caterpillars this spring, with municipalities and entomologists across the province confirming that populations have spiked dramatically in recent weeks.
Clusters of the small, distinctively patterned larvae are showing up on trees throughout Calgary and surrounding communities, prompting questions from homeowners and park visitors about what's going on — and whether there's anything to be done about it.
What Are Forest Tent Caterpillars?
Despite their name, forest tent caterpillars don't actually build tents. They're known for forming dense, writhing masses on tree trunks and branches, which can be alarming to stumble upon on a morning walk.
The species is native to North America and feeds on the leaves of deciduous trees — favourites include trembling aspen, birch, and oak. During outbreak years, infestations can be severe enough to completely defoliate trees, giving entire neighbourhoods a strangely bare look in the middle of spring.
Entomologists describe the current Alberta surge as part of a well-documented cyclical pattern. These outbreaks typically build over several years before population collapse — often triggered by disease, parasites, or starvation — naturally resets the balance.
Should You Be Worried?
The short answer: probably not. While a heavily defoliated tree looks alarming, most healthy trees can survive one or even two seasons of significant leaf loss. The damage is largely cosmetic, and foliage typically grows back.
Municipalities are advising residents to avoid pesticide use where possible, as broad-spectrum insecticides can harm beneficial insects — including the natural predators and parasites that ultimately help bring outbreaks under control.
For homeowners with particularly vulnerable or ornamental trees, wrapping trunks with sticky barriers can help prevent caterpillars from climbing up. Burlap bands that trap caterpillars during the day can also be effective for smaller trees.
How Long Will It Last?
Outbreaks of this kind typically peak over a two-to-three year period before collapsing. The caterpillars eventually pupate and emerge as moths in midsummer, laying egg masses on tree branches that will hatch the following spring.
Experts say the cycle, while frustrating for residents and unpleasant to look at, is a normal and natural part of the forest ecosystem across Canada — particularly in the boreal and mixed forests that stretch from Alberta eastward.
It's worth noting that similar outbreaks have occurred in Ontario and Quebec in previous years, so if you've seen the footage of caterpillar-covered trees circulating online, it's likely not the first time Canada has dealt with this.
The Bottom Line
This spring's caterpillar explosion is a natural phenomenon — messy and a little unsettling, but nothing to panic about. If you're an Albertan watching your backyard trees get stripped bare, experts say the best course of action is patience. The caterpillars will move on, and your trees will likely bounce back just fine.
Source: CBC News (CBC Top Stories RSS feed)
