Blinded by bias

I now see that these assumptions affected how I spent my time in the field — where, when, and in what habitats I looked.

a spotted-wing grasshopper. — Photo by Matt Pelikan

In observing nature, one goal is to see what’s truly there, and not impose your own wishes or expectations on the world. The classic example of what to avoid is the sort of wishful thinking to which birders can be subject. It’s easy to see field marks that don’t exist if you’re burning to find a rarity, and equally easy to miss a rarity because you’re expecting just the common stuff.

But even when you have no personal stake in what you see, it’s still possible for benign assumptions or inaccurate knowledge to distort what you see. Though I’ve had more than 40 years of practice in trying to be an impartial observer of nature, I can’t say I’m never guilty of making errors of this sort. I like finding a rarity every bit as much as the next guy, and I’m just as prone to ignorance. So it doesn’t surprise me too much when I find I’ve botched things. And so it was with me and the Gomphocerinae.

“Gomphocerinae” is a mouthful, but it’s shorter than the usual common name for this family of grasshoppers, “stridulating slant-faced grasshoppers.” They stridulate, or produce sound, by rubbing body parts together, and species within this family tend to have faces that slant sharply down and back from an overshadowing forehead.

In beginning my ongoing survey of Vineyard grasshoppers, I had drawn up a list of species I felt were possible here, based on range maps in field guides. And I now realize that, even as I drew up that list, I began forming misconceptions about the grasshopper species that I would find. Some that were familiar to me from my mainland days I thought of as common, and I assumed, without any real basis in fact, that I’d find them here, too. Certain other species, such odd-looking ones or ones that have unusual life histories, I now realize I classed as “exotic” — rare or specialized species that I couldn’t imagine occurring here.

To some extent, I now see, these assumptions affected how I spent my time in the field — where, when, and in what habitats I looked. And one group that I had unconsciously decided wasn’t worth sinking much time into was the Gomphocerinae, those grasshoppers of the stridulation and the slanting faces. But it wasn’t just a time allocation error: when trying to identify grasshoppers, I tended to start with the assumption that what I was looking at belonged to one of the families I expected.

Thus it was that my grasshopper list, closing in on a dozen species as this season began, lacked any representative of Gomphocerinae. But about a month ago, while tidying up my office at work, I came across a box of insect specimens labeled “Orthoptera.” These turned out to be the result of field work done 20 years ago; the specimens were meticulously mounted and labeled with date and location information but had not yet been identified.

The first thing I noticed was, you guessed it, a prime example of a stridulating slant-faced grasshopper — an “exotic” species I had offhandedly tossed in the “impossible” bin. It was a short-winged toothpick grasshopper, a bizarre, elongated insect with sword-like antennae and ludicrous stumpy wings. I had never imagined I’d find it here, even though its habitat is one that is easy to find on the Vineyard: dry, sparse, “bunch grass” habitat dominated by little bluestem. Bunch grass just hadn’t looked like good grasshopper habitat to me, and accordingly, I hadn’t explored it much.

I may have made some wrong assumptions, but you may be sure that at this point I was realizing that I had made them. I altered my strategy based on what I had learned and deliberately targeted a number of Gomphocerinae associated with bunch grass. First, I quickly located another location that had that most excellent toothpick grasshopper; here weren’t a lot and they were not yet mature, but this is a bug you can’t mistake.

I also found and photographed a second member of the family, a spotted-wing grasshopper, a nondescript bug that in years past I may well have written off repeatedly as a dully marked member of a different family. (They turn out to be common, common!) Finally, I went back through my file of unidentified grasshopper photographs and quickly picked out another member of Gomphocerinae, a lovely green species called the pasture grasshopper.

Better still, I began to get a sense for the entire family: what conditions its members like, what characteristics mark the family itself or help you sort out its members. In short, I learned something! I find this fun.

There are, presumably, other biases and misconceptions lurking in my understanding of grasshoppers (not to mention the other types of wildlife I observe). I haven’t discovered them yet, but with luck I will eventually. There’s always a moment of dismay when you realize what a bonehead you’ve been. But having realized it, at least you can get things right in the end.