A caterpillar makes its way along a concrete sidewalk in Saanich. (Don Descoteau/News Staff)

A caterpillar makes its way along a concrete sidewalk in Saanich. (Don Descoteau/News Staff)

Tent caterpillar season in Greater Victoria sees gardeners fight for their foliage

Manual removal method the easiest, but targeted natural insecticides available

The silky sacks in trees are back.

It’s the time of year when home gardeners and professionals alike are finding colonies of western tent caterpillars on the ends of branches, in deciduous trees such as willow, poplar, plum, apple, cherry and oaks, and occasionally bushes. While the fuzzy creatures, which ultimately transform into moths, are not an invasive species – they are native in various forms around North America – people looking to keep their trees and rose bushes lush, green and healthy routinely take steps to get rid of the voracious, leaf-eating caterpillars.

Glenn Harris, senior manager of environmental protection with the Capital Regional District, said tent caterpillars’ numbers naturally cycle – eggs are laid once a year by females – and they do little harm to a tree other than defoliation. He suggests nest removal should be done by hand, and that pesticides are not necessary to control this species.

Health Canada recommends that for best effect, removal of the tents be done when the caterpillars are at rest, in the early morning, late evening or on cool rainy days. Pole pruners can work well to remove the tents higher up in trees.

While many people choose to drown the caterpillars in buckets of water once removed from the tree, there are other options to prevent defoliation. The biological insecticide Bacillus thuringiensis, or B.t., sold under various brand names at major local retailers, can be sprayed on foliage once the first signs of leaf damage appear. As the bacterium is designed for use specifically against the larvae of moths and butterflies, it does not affect other insects and is non-toxic to mammals, birds and fish, according to Health Canada.

For homeowners who wish to let nature take its course, caterpillars are on the menu for some birds, including robins, blue jays and red-winged blackbirds. Also, yellow jackets and parasitic wasps are predators.

For other information about western tent caterpillars and controlling infestations, visit canada.ca/en/health-canada/services/pest-control-tips/tent-caterpillars.html.

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