I visited Colorado recently and, while hiking in the mountains, I was shocked to see the damage done to the forest. I had an eerie, sinking feeling as I looked out at huge swathes of brown, dead trees. And it wasn’t hard to figure out the culprit: trillions of individuals of a particular caterpillar species. Not only the trees, but the granitic rocks and gravelly paths were literally dripping with these lepidopteran larvae. I didn’t know the species, but I had a strong suspicion that it was invasive, and it was clearly doing a lot of damage to the forest.
I was taking a lot of photos, but one couldn’t miss this plague…hikers passing by asked me questions about it, able to somehow detect without asking that I was an ecologist.
It wasn’t hard to figure out what the pest was after I had access to a computer and the internet. I was definitely wrong about it being invasive…it’s a native species, but it has cyclical population outbreaks. There are even news stories about its sudden population boom and the potential effects (e.g. increased wildfire risk in spite of the unusual amount of rain they’re receiving).
This is the Douglas Fir Tussock Moth (Orgyia pseudotsugata):
It’s a pretty little thing, but it’s causing a lot of damage.
Damage to the trees…notice the green oaks in the foreground and the dead looking spruces and firs in the background.
Cocoons and larvae in the tree
Interestingly, the females are flightless…now I wish I’d looked closer to see if I could find a female!