Elm spanworms swarming parts of downtown Winnipeg are about to get a blast of BTK.

The City of Winnipeg is planning to douse the crawling critters with the biological insecticide on Friday morning.

"It will probably take us about an hour to an hour-and-a-half to treat that and they'll feed on it and then they should die in about 48 hours," said Ken Nowalsky, the city's superintendent of insect control.

The spanworms, which are devouring tree leaves and coating everything in webs along Assiniboine Avenue between the legislative building and Carlton Street, can reproduce at an impressive rate with each female capable of laying as many as 250 eggs.

Nowalsky said the worms are usually seen in Charleswood and this is the first time they've been seen in the downtown.