A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

If I hadn't killed 52 flies as a child, how many descendants would they have had by now?

August 29, 1980

Dear Cecil:

As an only child, I was forced to be ingenious about inventing solitary diversions. While reading an old diary recently, I found that on July 1, 1969, I went on a murderous binge which resulted in the untimely death of 52 houseflies. Knowing how degenerate their reproductive habits are, I got to wondering how many of their descendants would be around to plague us today had it not been for this prodigious feat of dipterocide. Can you enlighten me? For obvious reasons, I prefer to remain …

Dear Anonymous:

If it's awesome statistical fireworks you're looking for, buddy, you've come to the right place. The female Musca domestica, or common housefly, typically lays 600-1,000 eggs in the course of her roughly two-month lifetime, most of which grow to maturity in 10-12 days, whereupon they can set about raising little maggots of their own. Under ideal conditions (which invariably prevail in this column), you may get as many as 12 generations a year.

Let's suppose that 132 generations would have been born, or laid, or whatever the appropriate term might be, had you not committed the aforementioned massacre 11 years ago. Let's further suppose that half of the 52 flies were female, that half of all subsequent generations were female, and finally that each female deposited 1,000 eggs.

The total number of female descendants would be 26 x 500132, and the total fly population, naturally, would be twice that many. Having performed various subtle mathematical manipulations on my handy calculator, I may categorically state that your house would presently be infested by roughly 9.550892 x 10357 flies. At 128 flies to the cubic inch, we get 3.25 x 1016 per cubic mile, or 2.292 x 1056 per cubic parsec, which means that all the flies would fit into a cube a little more than 3.45 x10100 parsecs on a side.  The galaxy in which we presently reside, for comparison, is 25-30 parsecs across. It's easy to scramble up your decimal points in calculations of this type and I may have lost track of a few billion parsecs here and there, but the implication in general is clear: With that selfless act long ago, you single-handedly saved the cosmos.

The lesson in all this, of course, is the futility of trying to predict the future by projecting a single factor. Most fly eggs, fortunately, don't survive till senior citizenhood, succumbing at some point to parasites, disease, predators, or starvation. Northern winters finish off whatever adult flies haven't been killed by something else, leaving only those in the larval and pupal stages to maintain the Muscidate race. The humbling truth is that, regardless of your efforts in the way of wholesale slaughter, at any given time there are about as many flies as the planet has room for, ecologically speaking. It's enough to drive you to racquetball.

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