Sample of European fire ants collected by Invasive Species Council of Metro Vancouver staff to send for verification. Fire ants are very attracted to apple.

Swarming ants join list of alien invaders plaguing southwest B.C.

Hogweed, knotweed remain major targets for weed eradicators in Metro Vancouver

While plants like Japanese knotweed and giant hogweed continue to menace the Lower Mainland, European fire ants that swarm and sting people and pets are a growing cause for concern among invasive species watchers.

Jennifer Grenz, development and projects manager for the Invasive Species Council of Metro Vancouver, said the dangerous ants were confirmed here more than a year ago and have been found multiplying across the region at sites in Burnaby, Vancouver, Richmond, the District of North Vancouver and Chilliwack, as well as Victoria.

“The ants can sting you and they swarm very quickly when they detect any ground movement,” Grenz said. “It’s not just one ant – you’re swarmed so there are going to be many ants on you.”

They’ve caused significant reactions in some people, Grenz said.

Dogs and horses can also be attacked by legions of the small red ants, which are hard to distinguish from the many other ant species found in B.C.

“It’s really their behaviour which is the defining characteristic,” she said. “This is the latest public safety concern for us.”

The council’s website, www.iscmv.ca, explains how to collect a sample of suspect ants and send it for free identification by B.C.’s agriculture ministry.

Grenz said residents have found themselves battling huge numbers of the ants because there are often multiple nests in close proximity – up to five or six in a single square metre of soil.

She suspects fire ants are being trucked around the region in contaminated soil that gets dumped at one site and used as fill or landscaping soil somewhere else.

They’re thought to have arrived in potted garden plants from Europe.

Grenz advises homeowners to carefully check any new garden plants, compost or top soil for ants before adding it.

European fire ants have formed more aggressive colonies in Canada than in their native Europe, according to a report of B.C.’s Inter-Ministry Invasive Species Working Group.

It says they have potential to spread inland to Hope and throughout the B.C. coast as far north as Prince Rupert and warns they can make yards “unusuable” for children and pets.

Meanwhile, weed control crews and volunteers are in high gear trying to eradicate giant hogweed.

The 15-foot towering plant is entering its flowering and seeding phase and Grenz said stopping the 100,000 seeds per plant from reaching the ground is critical to battling the spread.

“We’ve found more hogweed this year than ever before,” she said, but added public awareness is good and local municipalities and community partners are getting more effective at controlling the plant.

The sap of the giant hogweed contains a phytophototoxin that can cause painful recurring third-degree burns on the skin for up to 10 years after exposure.

“Any time your body is exposed to sunlight, that burn occurs again,” Grenz said.

It’s been found growing in Metro Vancouver parks in close proximity to playing children.

Homeowners can remove hogweed themselves – carefully, following the suggestions on the council’s website – but many opt to hire contractors.

Japanese knotweed, an imported shrub that can grow right through concrete foundations and roads, is more of an economic threat.

“We’re seeing it start to grow all over the region,” Grenz said. “It’s not really localized to a specific area.”

Grenz said several road and other infrastructure projects this year were delayed to allow knotweed treatment first.

It can’t be removed mechanically as a tiny segment of the plant can regenerate and there are often extensive root systems underground that can spread great distances laterally.

Instead herbicides are used – either by spraying the plant or injecting directly into the stem.

There’s growing concern among land owners and buyers of the risk of damage from knotweed and potential loss of property value.

Grenz said one potential option is to require the disclosure of the presence of knotweed as a known deficiency when properties change hand.

“It isn’t required right now but I wouldn’t be surprised if it is soon.”

In the U.K., where knotweed is an even bigger problem, insurers and lenders may refuse coverage or mortgages on properties with knotweed.

“That could become a reality here too,” she said.

Giant hogweed can grow up to 15 feet tall and release 100,000 seeds from a single plant. Its sap can cause skin burns that can recur for years.

Japanese knotweed taking over a North Vancouver street. Jennifer Grenz photo

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