News / Winnipeg

'Perfect storm' of worms nearly over in Winnipeg

The city's Insect Control Branch is expecting the creeper crawlies to hunker down and become moths soon.

A canker worm is pictured here on an oak leaf.

Gary Yokoyama/The Hamilton Spectator

A canker worm is pictured here on an oak leaf.

It’s been a weird, “perfect storm” of wriggly worms in Winnipeg so far this summer, but we're through the worst of it, according to the city’s top expert.

Insect Control Branch manager Ken Nawolsky said it’s “highly unusual” for populations of forest tent caterpillars, elm spanworms and canker worms to peak simultaneously, but that’s what happened this year.

“This is an anomaly… (like) nothing that we’ve seen before,” Nawolsky said. “Typically, when one species peaks, the others are at low levels… This year, we found forest tent caterpillars were at high levels, then elm span and canker worms were at moderate levels.”

But as bad as it’s been—with many of the city’s more treed neighbourhoods being overrun with the tree pest caterpillars—Nawolsky said Winnipeg’s out of the proverbial woods now.

“There’s only a few more days left (of caterpillars), after that you’ll see moths flying around,” he said, adding he expects the city to conclude its spraying program meant to control populations by Friday, after which trees freed of feasting bugs will begin to regrow lost foliage.

Though moths will emerge likely in early July to lay eggs that contribute to the next generation of the three bugs, Nawolsky said there will be some relief in the future as forest tent caterpillars are nearing the end of their life cycle in the city.

“Basically they come every 10 to 15 years and last for about three years, then their population crashes,” he explained. “Next year, we are expecting the canker and elm spanworm to increase in their numbers… but we are expecting a crash in population of the forest tent caterpillars.

“This is the third year, our peak year for forest tent, this should be the end of their life cycle and then we won’t see them for a number of years.”

Forest Tent Caterpillars

· Size: Adults are roughly 45-55 mm long

· Appearance: As caterpillars, they’re bluish to brownish in colour, with diamond-shaped white spots and a fuzzy body

· Frequency: Three year spike every 10 to 15 years

· Lifespan: Approximately six to seven weeks  

Elm spanworm

· Size: Adults are usually 50 mm long

· Appearance: Most bodies are normally somewhere between slate grey and brownish black, and the head is rust-coloured, but others are lighter green with yellowish heads

· Frequency: Insect Control Branch manager Ken Nawolsky said they’re “kind of unpredictable,” and the population can rise and fall dramatically from year to year

· Lifespan: Four to six weeks

Canker worms

·  Size: Spring and fall cankerworms are both about 25 mm long

· Appearance: Colours range from light green to brownish green, often marked with a darker stripe down their back

· Frequency: Populations peak about every seven years, Winnipeg has had low cankerworm populations for the last three years

· Lifespan: Roughly six weeks

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