Tent caterpillars remain in boom cycle in Saskatoon, cankerworms normal

Once again, it’s the year of the forest tent caterpillar in Saskatoon.

Moths have laid their eggs in trees across the city and soon thousands of the tiny black, green, yellow and white insects will start nibbling on the leaves.

The good news is the bugs are relatively harmless.

City of Saskatoon pest management supervisor Jeff Boone said tent caterpillar outbreaks come in cycles of three to seven years, and this is the third year they have seen a jump in numbers.

The city received lots of calls about tent caterpillars the last two years, so Boone is not surprised they have received even more calls this year.

He said the city does not trap or spray the bug and has no official numbers.

Tent caterpillars’ favourite foods are Green Ash and Chokecherry trees, but they will eat just about any kind of leaves. The small bugs gather in large numbers and can be unsightly.

Boone said the caterpillars are known as a “cosmetic insect” and their damage to trees is minimal.

Trees would require several years of high defoliation before they would suffer. Tent caterpillars feed quickly and by early July, most are in their cocoons or have turned into moths.

The best way to get rid of tent caterpillars is to spray them with water to knock them off trees and homes. If the water does not drown them, they are then easier to squish on the ground.

Boone said cankerworms and leafrollers are out this year, but in relatively normal numbers.

“We haven’t had any significant number (of cankerworms) since 2008,” Boone said. 

“The one exception would be Woodlawn Cemetery, where there’s recurring cankerworm population just because of the high number of elm trees.”

Tree banding can prevent cankerworms, but won’t stop tent caterpillars and leafrollers.

They should be placed on trees from September to May so the bugs can’t lay their eggs in the fall and spring. Bands should be removed before June because moisture under them can cause the tree to rot.

Residents should also be on the lookout for the deadly Dutch Elm Disease, Boone said. The city had one case last year and will check on elms throughout the city this summer.

Boone said residents should watch for wilting and yellow leaves in July, and should observe the pruning ban lasting from April 1 to Aug. 31.