In late autumn there is alternate way to measure one’s vehicle speed down a country road other than mph. You can use the cpm method. On the outside chance that you have not heard of this, cpm stands for “caterpillars per mile.” And, on the even slimmer chance that you don’t know what I am talking about, please allow me to explain (or attempt an explanation without hurting myself).
The caterpillars in question are the famous larvae of the Isabella Tiger Moth better known as Woolly Bears. You know, those fuzzy black and red fellows who are believed by some to prognosticate winter weather. Note that I said “are” rather than “were” in the previous sentence because there are a few believers that stick to this fantasy to this day. Of course, not everything you believe in comes true (for instance, I believe that someone will come up to my door someday with a huge silver tray loaded with unimaginable riches and offer it to me). Such unverified beliefs are called folk tales – they are fun as long as they are kept “folksy.”
In truth, if the Wooly Bear could predict winter weather it most certainly would. These larvae overwinter as caterpillars so it would be nice to know what kind of winter to expect. But, alas, they have no more idea than we do and so they dash about like headless chickens just before the hard frosts hit. On sunny fall days, you will see herds of them darting across the road – just to get to the other side (obviously inspired by those headless chickens to do so). They are seeking hibernation sites, but still it seems like a very random process. Oh, in case you take exception to my use of the word “darting” in reference to caterpillar motivation, please hold on a minute because I will get to that.
The point is that on those special sunny days you will often see so many of the road-crossing Woolly Bears that you can literally measure your forward progress by counting them. This is the where the cpm rating comes in. I recently recorded a cpm of 10 while driving down 3 miles of a parkway. There were approximately 10 caterpillars for every mile of roadway. My mph was around 15 and my progress resulted in a ccpm rating of approximately 1 – that’s one crushed caterpillar per mile).
The amazing thing about watching Wooly Bears is that you will notice how fast they really are. I’ve read that these fellows can clip along at .7 mph. For a two inch critter with 16 legs this is a pretty good pace. In fact, I thought that number might be a folkloric figure rather than an actual one. You can’t believe everything you read (I offer my blog as living proof of this principle). No, I needed to verify this somehow.
I don’t own a speed gun, and was not about to corner a local policeman and ask him to clock a caterpillar with his radar gun. I felt that this request would have been misinterpreted. So, I went straight to the field, employed a local Woolly Bear to walk the walk (see the movie clip here), and then hit the calculator. My math skills are legendary – as in folkloric, or imaginary if you prefer – but I pulled out all the numbers I could manage (see my figures below if you don’t believe me).
Figuring that my subject walked a set distance in the set time allowed, and taking into account that it was a Tuesday and that the moon was waning, I divided the co-sine by the sum total of the weed whacker, and arrived at a figure of .6 mph. Even considering my considerable margin of error (more like an expressway of error) this was amazingly close to the published figure. Further considering that the published figure was probably drawn from the use of a real radar gun (the same gun that once clocked a stationary woodlot going 90 mph), I was satisfied. Woolly Bears can haul their little bear butts at an average rate of .6-.7 mph.
Unfortunately, the cpm rate will soon be down to 0 when the snow starts to fly. So, no one will have a good opportunity to prove me wrong until next year. Gee, that’s too bad.