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Grasshopper statistics don't lie, but...

Q: Quoting from your answer about active grasshoppers: A hefty density, like six or seven adult grasshoppers per square yard, eat as much as a cow does. It's hard to imagine such a thing - even with a small cow. -- Ed W.

A: You have a nice skeptical attitude towards statistics. It turns out the statistic is ball park correct and actually a little conservative but there is a lurking factor or two.

[Corel] "Roping a Maverick" by Seltzer

I got that statistic from Jeffery Lockwood, entomology professor at the University of Wyoming: a knowledgeable guy with a flair for memorable quotes. I asked Jeff how he computed the figure after I read your question.

Jeff says a cow eats 30 pounds in a day. So, first we calculate how many grasshoppers eat as much as a cow. A decent-sized grasshopper eats at least 0.1 grams (0.0002188 lb) of food per day. Thus, for one day, thirty pounds of food supports 137,111 grasshoppers (30 lb / 0.0002188 lb). That's a lot of grasshoppers.

Then we look at densities and areas. If one grasshopper eats 0.1 g, then a density of 6 or 7 grasshoppers per sq. yd. eat 0.6 or 0.7 grams per sq. yd. But note: we're talking about a small area-- 1 square yard. That's the misleading lurk.

However, we're really interested in the area needed to feed that big number (137,111) of grasshoppers. At a density of 6.5 grasshoppers per square yard, that grasshopper horde needs an area of 21,094 square yards (137,111 grasshoppers / 6.5 grasshoppers / sq. yd.) or 4.36 acres of the voracious pests.

Jeff lives in Wyoming where it takes about 5 acres to support a cow with the required 30 pounds of fodder, but 5 acres of grasshoppers (at a density of 6.5 per sq. yd.) will eat 34 pounds of food (30 x 5 / 4.36). So the grasshoppers do eat more than the cow.

(Answered July 19, 2002)