They're eating leaves, dripping from trees, trailing silky threads and crawling on unsuspecting pedestrians.
The elm spanworm, another type of tree-pillaging caterpillar, has infested a downtown area along Assiniboine Avenue between the legislative buildings and Carlton Street.
Help is coming soon, though.
Ken Nawolsky, the City of Winnipeg superintendent of insect control, said a crew will spray the creepy crawlers tomorrow, weather permitting.
"The elm spanworm, these worms tend to make an appearance about every four to five years, in different parts of the city," he said.
"Normally they are in the Charleswood area, we've noticed them now in the downtown area."
He said the concentration of the worms seems to be backing onto the Assiniboine River to Broadway. Edmonton Street between Broadway and Assiniboine Avenue is crawling with the creatures.
The worms are covering some parking meters, clustering on apartment building walls and doorways and dropping onto the heads, arms and backs of passersby.
The elm spanworm has the propensity to cause "total defoliation" in an area and has a "spider web look hanging down on silken threads," Nawolsky said.
"The city, weather-dependent, will go out around four in the morning and spray that four-block area with a biological product called BTK," he said.
Nawolsky said it's expected the elm spanworm will eat the biological product and die within about 48 hours, with no harmful effects to birds or other organisms.
He said the elm spanworm typically shows up in isolated pockets of neighbourhoods, while the forest tent caterpillar is more widespread. Forest tent caterpillars are more of a general feeder and they'll even eat shrubberies.
In a week's time, the worm's life cycle will end. They burrow in the ground to pupate and emerge as moths.