Tent Caterpillars in Alberta: How to Identify them and Protect your Trees
As spring turns into summer across Edmonton and St. Albert this year, many homeowners might begin to notice silky webbing and clusters of caterpillars gathering in their trees. These are likely tent caterpillars, a common seasonal pest in Alberta that can quickly become concerning when populations grow.
While tent caterpillars are not usually fatal to healthy mature trees, repeated infestations and stress can weaken tree health over time, especially when combined with drought, storm damage, or existing disease.
Here’s what you should know about identifying tent caterpillars, understanding their impact, and supporting long-term tree health.
What Are Tent Caterpillars?
Tent caterpillars are the larvae of moths that emerge in spring and early summer. They are known for creating large silk nests, or “tents,” in the branches of trees where they gather for warmth and protection.
In Alberta, they are commonly found on:
- Trembling Aspen and Poplar trees
- Chokecherry/Mayday trees
- Apple and other fruit trees
- Birch, Ash, and Maple trees
The caterpillars feed on leaves, sometimes stripping branches bare during heavy infestations. Severe infestations can see the caterpillars spreading beyond trees to gardens and other plants.
How to Identify Tent Caterpillars
- Silk Webbing in Branches
The most recognizable sign is the white or silvery webbing built in tree crotches and branch unions. - Clusters of Caterpillars
Tent caterpillars travel and feed in groups, often gathering together on trunks and branches. - Defoliation
Leaves may appear chewed, sparse, or completely stripped from sections of the tree canopy. - Increased Activity in Spring
Infestations are most noticeable during late spring and early summer when larvae are actively feeding. - Visually
Mature caterpillars are 50mm long, with blue stripes along the sides and a long, whiteish spots along the back.
How Dangerous are Tent Caterpillars?
In many cases, healthy trees can recover from occasional defoliation. However, repeated infestations or additional environmental stress can weaken trees significantly over time.
Trees already affected by winter damage, drought stress, poor pruning, compacted soil, or disease or decay may struggle to recover as easily.
Weakened trees can become more vulnerable to branch dieback, slower growth, fungal issues, and secondary or future pest problems.
What Homeowners Should Do
- Avoid Damaging DIY Removal Methods
Burning nests or aggressively cutting branches can sometimes create more damage than the caterpillars themselves. - Safe Removal of Eggs and Caterpillars
Egg bands can be found in early spring before leaves, and are shiny, hardened, band-like masses that encircle branch. They can be easily scraped off with a dull blade. Caterpillars can be picked off by hand and placed in a bucket of soapy water, or sprayed off with a strong garden hose blast. - Always Monitor Tree Health
Keep an eye on canopy density, dead branches, leaf regrowth, and the overall tree condition throughout the season. - Prune Damaged or Dead Limbs
Proper pruning can help improve tree structure and remove weakened growth caused by stress or previous damage. Contact HML Landscape & Tree Services to schedule a professional tree assessment or pruning consultation with our arborist team. - Support Overall Tree Health
Healthy trees are more resilient against seasonal pests and environmental stressors. Proper watering, mulching, and routine assessments can help support long-term health.
Local Resources on Tent Caterpillars
Tent caterpillar activity can vary year to year across Alberta, typically in cycles of 7 – 10 years. For additional information and local updates, you can review resources from the City of Edmonton, Parkland County, Alberta’s Forest Tent Caterpillar Defoliation Forecast Survey, and Natural Resources Canada.
You can also read more about recent tent caterpillar activity across Central Alberta through Central Alberta Online.
When to Call an Arborist
If your trees are showing signs of decline, repeated defoliation, dead branches, or structural concerns, it may be time for a professional assessment.
At HML Landscape & Tree Services, our ISA Certified Arborists help homeowners throughout Edmonton, St. Albert, and surrounding areas assess tree health, identify structural concerns, and recommend proper pruning and maintenance strategies to support healthier, safer trees.
If you’re concerned about tent caterpillars or overall tree health this season, call us to schedule a professional tree assessment or pruning consultation with our arborist team.
