Sunday, November 6, 2016

Is Dave a "Giant" Earthworm?

I loved this story this week about Dave the Giant Earthworm. The mind sort of boggles at a 40 cm worm. How did "he" get so big, people were all asking. There must be some limit to the maximum size an earthworm can reach, and helminthologists* have tried to find the upper limit by raising them in lab conditions optimized for growth. But they still have never seen one as big as Dave.

Outliers like Dave are extremely interesting. We often want to consider what the limits are on things like earthworm length because it helps us to define what an earthworm is. Finding one well outside the normal bounds of length seems pretty important. But is it? I mean, it's not like we're systematically sampling earthworms for size, and we've probably only been keeping track for maybe 100 years or so. So finding a great, big one will happen rarely, but it certainly doesn't mean that earthworms are getting bigger.

The longer we observe something for, the more likely we are to see outliers like Dave. But the more observations we have, the better we are at characterizing a distribution overall. We might have been able to predict that a worm like Dave existed if we'd been able to see a distribution (a histogram) of existing observations of worm length. The next longest worm ever documented was 39.6 cm, so it isn't reaaallly that much longer than another worm we already knew about.

Still, 40 cm is a really long worm. I'm glad it made the news.

* I've since learned that helminthologists study parasitic worms, not earthworms. It's still a great word but I've apparently misused it here. They're called Oligochaeteologists!

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