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We have started to notice Tent Caterpillars in the County this spring. Typically, the caterpillar’s population booms approximately every 10 years in Alberta. Healthy trees can handle light defoliation and will leaf again in the season, and most trees are well adapted to caterpillar damage.

  • Caterpillars have blue stripes down their body, with white keyholes shapes down the backs.
  • The eggs overwinter in masses in a ring around a branch containing 100-350 eggs. Hatching occurs in spring when the trees’ buds begin to swell.
  • Larvae make web tents to protect themselves.
  • The caterpillars feed on deciduous trees, preferring trembling aspen and poplar, but can also feed on birch, ash, apple and fruit trees, cotoneaster shrubs and can spread to garden crops in years of heavy infestation.
  • There is one generation a year.
Management:

Management is typically not necessary due to the short timing of outbreaks, and birds, large ground beetles and other predators keep them in check.

Removing Egg bands from infested trees and shrubs by scraping with a dull blade – most easily seen in the fall prior and spring before leafing out. They can be left away from the trees so other animals can eat the larvae as they emerge, or the larvae will starve. 

Clusters of caterpillars can be removed with a strong jet of water or put in a bucket with water and disposed of once dead.

Silk webs can be removed with a stick or in some cases pruned out of the tree. If nest is destroyed, most often the caterpillars knocked on the ground will die before they can make it back up the tree.

Bacillus thuringiensis (BTK) can be applied to foliage while larvae are small in May, which they will eat then die. BTK affects all caterpillar species but is generally safe for animals, fish, birds, pets and children.

Cocoons in June and July can be manually removed and disposed of in a sealed bag.

As a last resort, Malathion Contact Insecticide can be used for ornamental trees – read and follow the label correctly. The insecticide must make contact with caterpillars to be effective.

Parkland County does not control Tent Caterpillars on Private or County-owned lands, but if you would like to report them, you are welcome to call the Agricultural Services Desk at 780-968-8467. 

References:

https://www.edmonton.ca/programs_services/pests/forest-tent-caterpillars

https://www.canada.ca/en/health-canada/services/pest-control-tips/tent-caterpillars.html

https://www.strathcona.ca/agriculture-environment/plants/tree-care/tree-pests/

https://www.sasktoday.ca/north/opinion/forest-tent-caterpillars-now-what-4121378