The caterpillars are black, grey, or white with an orange stripe running longitudinally across the body.

Moths are brown, yellow, tan or grey, with two lighter or darker lines crossing the body.

[7] Western tent caterpillars are ectothermic, therefore they do not produce their own body heat and are heavily influenced by environmental temperatures.

Larvae are thought to thermoregulate by basking in the sun and staying in close groups to elevate body temperature.

Aggregations of caterpillars help discourage predation, increase temperature, and facilitate foraging.

During late instars, caterpillars get larger and require more food resulting in more solitary behaviour.

[9] Caterpillars flick their heads in response to the sound of fly parasites, as a defensive mechanism.

Additionally, caterpillars can contract NPV by coming in contact with silk strands from other larvae.

[4][6] Outbreaks of western tent caterpillar can cause large scale defoliation of trees.

However, outbreaks of larvae are considered to be more of a nuisance than a problem and does not negatively affect forest health because trees are able to regrow leaves quickly.

[6] Human suppression of western tent caterpillars is most successful when intervening before high population numbers are reached.

[3] Due to effects of climate change it is predicted that there will be a phenological asynchrony between host tree and the western tent caterpillar, characterized by advancing larval emergence.