Butterflies as Pests?

Yesterday this innocent-looking white butterfly landed on a coworker’s hard hat and I made her stand still so I could take a photo before it flew away.

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This is a male Pine ButterflyNeophasia menapia. I first became aware of their existence shortly after moving here, when I noticed a brochure tacked up on the wall at my office – an update from the previous year on a Pine Butterfly outbreak in the local national forests. Like many butterflies, these are tied to a specific plant to complete their life cycle – in this case, their caterpillars feed on the needles of Ponderosa Pines and Douglas-firs. Unlike many butterflies, they occasionally have large outbreaks that can damage forests, which happened here last year. (Incidentally, the Forest Service brochure reassured anyone reading it that despite the damage “…they are not ‘eating all the trees,'” and I felt like those quotation marks conveyed a lot of frustration and weariness on the part of the Forest Service staffer tasked with educating the public on this issue. Doubtless he/she had fielded a lot of phone calls from people demanding that the agency do something about those butterflies eating all the trees.)

Anyway, I’m not used to thinking of butterflies as pests, but people around here who know almost nothing else about butterflies seem to know that white butterflies eat pine trees. (I’ve already found myself explaining at least once that no really, there are a lot of different kinds of white butterflies and only one actually eats pine trees, so please, please don’t just smoosh any white butterfly you see). The outbreak has died down somewhat since last year, and today was the first time I’d actually spotted any of the butterflies in question. It got a fair amount of media coverage at its height, though, including this great NPR piece complete with video of the butterfly “snowstorm.”

I looked briefly for any signs of eggs or caterpillars on the needles of the trees around us, but without time for a more thorough search I wasn’t able to find any. In any case, like so many things in nature, these insects are a little more complicated than we might like them to be. Butterflies are nice, pests are bad – which one is this?