They're huge, hairy and will cause your skin to erupt with oozing blisters - and they're here.
For a second year, Caledon, Ont., has been invaded by giant hogweed, or Heracleum mantegazzianum, a towering plant that can grow to over six metres tall.
With its hairy stems, purple patches and huge leaves spanning up to three feet wide, the giant hogweed is also a menace to society - it secretes a clear, watery sap that can cause burns, blisters and even blindness, both temporary and permanent.
"The bottom line is, you stay away," said Louis Zidar, Caledon's manager of public works. "It's like 10 times worse than getting poison ivy on you."
Unfortunately, the nefarious weed also produces clusters of white flowers resembling Queen Anne's Lace, thus easily luring hapless plant lovers into its poisonous embrace.
"Of course, if the buds look beautiful, you like to touch them and hug them and cradle them and the next thing you know you've got the secretion on your skin," Mr. Zidar said.
Giant hogweeds originated in Europe and were likely brought to North America as ornamental plants.
They have since spread around Southern Ontario, mostly along roadsides and stream banks.
The weed is harmful to natural ecosystems and has been listed by Credit Valley Conservation as one of its top 10 invading species to target.
In Caledon this year, giant hogweed has been sprouting in at least four locations, Mr. Zidar said, with Brampton also reporting infestations. The town of Caledon has hired a pest management company to eliminate it and released a public notice yesterday warning residents to be cautious when handling the plant.
Residents were also advised to wear rain suits, gloves, boots and protective eyewear when attempting to remove the weed from their property.
Area resident Angela Meyer says the weed has been growing "quite wild" around her two-hectare property. Last year, her son, Simon Kyer, touched a giant hogweed and broke out in "big oozy things" measuring "inches long and wide," according to his mother.
The rash lasted a week and a half and was eventually remedied by a steroid cream prescribed by her son's doctor.
"I am not a fan," he said. "Don't pick it. Get rid of it, try to burn it."