I found this caterpillar trundling along the sidewalk at Athabasca Falls in Jasper National Park on 17 May this year. Noticing all the tufts and hairs I immediately thought, “I bet that’s irritating!”, so dropped to my knees, gently brushed it into a plastic vial and took it to the nearest picnic table for a closer look. I had no clue what its natural food plant was, so I took photos of it on a plain white background.
I released it soon after, placing it on a log where it was immediately noticed by an ant, which, ignoring the obvious defences and overwhelming size difference, moved into attack.
Unfortunately, my photographic observations were cut short by protests from wife Yuet, who noted that the caterpillar had no choice in the matter and that I was interfering with nature. The desire for marital harmony persevered over scientific discovery, so I rescued the caterpillar, photographed it again on white, and then placed it on a nearby (and ant-less) fir-tree branch, which satisfied She-who-must-be-obeyed. Noble fellow that I am, I refrained from pointing out that this was also interfering with nature, especially if the fir was the food plant. It turns out it was.
Pine Tussock Moth Caterpillars are conifer specialists, taking particular delight in eating fir (Pseudotsuga sp.) needles, but also partaking in pine (Pinus sp.), western hemlock (Tsuga heterophylla) and spruce (Picea sp.). They are normally rarely seen, but there are occasional outbreaks that can completely defoliate trees. Their range covers most of western North America, from BC/Alberta south to New Mexico. The adults (right) are somewhat lacklustre in comparison to the larvae.
In hindsight, I wish I had spent more time photographing the caterpillar at higher magnifications to get more details of the various hair tufts. I am also left wondering just how effective the tufts and hairs are for deterring predators and parasites. If anyone knows of any literature about these details, please let me know.
Thanks to Dave Holden of the Alberta Lepidopterists’ Guild for the ID.
Forestry Service, USDA (pdf)