I noticed an abundance of caterpillars, beyond anything I have seen in a single hike before. Taking over Kesugi ridge, I’m not a local but discussed what I saw with individuals familiar with the trail and even the historic society at Talkeetna and no one seemed to be able to explain our weird encounter with these caterpillars. They were everywhere, covering the cairns marking the trail to the point that they appeared black from a distance due to the complete coverage of caterpillars. When we sat down, they swarmed our packs and bodies and were constant from coal creek to Byers lake. Only during the rain and at lower elevations did they let up. I don’t believe they are a natural occurrence based on our discussion with people familiar with the trail. Just wanted to give a heads up and maybe see if this was a new experience or a fantastical phenomenon that we happened to experience. Definitely worth some research.
This is a Rusty Tussock Caterpillar swarm, the pupa stage of the Rusty Tussock Moth. The USDA Forest Service has a profile for the specie here. These hungry hungry caterpillars are polyphagous and feed on such varied plant species as Birch (Betula spp.), willow (Salix spp.), Prunus, Sitka Spruce (Picea sitchensis), and many other conifers, hardwoods, and shrubs. Outbreaks of rusty tussock moths occur periodically and are typically short lived.
In 2020, noticeably high populations were reported in Southcentral Alaska in Hatcher's Pass and along the road system in the Matanuska-Susitna Borough. The only concern with this species is the hazard of dermatitis for those who have had bare-skin contact with them or foliage they have shed on. The little bristles on their backs can get into the skin and cause irritation and itchiness. One instance of this occurred among berry pickers who reported the caterpillars feeding on blueberries, cloudberries, currants and highbush cranberries, among others. There have been similar swarm events in Nome and other parts of Alaska. According to this article by the Nome Nugget:
"Alaska has seen infestations in the Mat-Su Valley in 2010 and there have been outbreaks in 2003 and 1997. In the Mat-Su 55,000 acres were affected but damage to vegetation was not permanent."
In the related posts tab, you can see the most recent swarm event in Nome in 2019 where Jessie Moan, from the University of Alaska Fairbanks Cooperative Extension, consulted on the other observation about caterpillars, saying:
"The caterpillars are tussock moth caterpillars. They are known to feed on a variety of trees and shrubs and can defoliate large areas when populations are high. Populations can vary from year to year depending on the weather."
Chyna Perez-Williams
Denali State Park