The Great Pill Bug Poll

Roly-poly, potato bug, chuggy pig, Granddad, butchy boy, pill bug – for such an unremarkable looking insect, this little guy has managed to rack up quite the number of nicknames all around the world. Except, for starters, he’s not an insect at all. Meet the woodlouse – a diverse group or animals that can be found all throughout British Columbia, from our forest floors to the little nooks and crannies of our garages. Woodlice are crustaceans, which means that they’re closely related to animals like shrimp and lobster.

For this week’s lab, we were taking a look at where woodlice choose to live. Specifically we were asking the question: what kind of moisture, temperatures and light levels do woodlice like the most? So on the first drizzle of the new term, the brave students of BIOL 326 ventured off to Pacific Spirit Regional Park to flip over some logs and count critters.

Kneeling down in the mud, picking up and counting squirming little woodlice may not be my most glamorous UBC academic experience, but it provided us with our first observation of the lab. There were way more woodlice on the bottom of logs then on the top. Clearly something was attracting the little guys to this one position on the log, and we had a guess as to why. So with Ziploc baggies full of captive woodlice, we headed back inside to the lab to run some experiments.

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Dark/light choice experiment

We suspected that there was some aspect about the under-log that was causing woodlice to live there – chiefly that it was dark, moist and cool. Were any of these three factors attractive to woodlice? Were all three? The only way to know for sure was to conduct a choice experiment. One-by-one, woodlice were placed in a container split right down the middle. Moist and dry, hot and cold, light and dark, the container had two halves that represented two choices in habitat. Wherever the woodlouse was standing at the end of two minutes would be considered its “choice”.

We put 24 different woodlice through each of the three choice experiments. What was the verdict? It turns out that woodlice really like cool and moist environments. Darkness? Not so much. 21 woodlice chose moist, and 20 chose cold – pretty strong evidence that they are attracted to that habitat type. In contrast, exactly 12 woodlice each chose the light and the dark sides of the container, hinting that the light level had no effect at all on which side they decided to choose. Just from that data, we can infer that woodlice like to live under logs because they are cold and damp.

Time and time again, the woodlice clearly favoured the colder bag of water on the right.

Time and time again, the woodlice clearly favoured the colder bag of water on the right.

I know this is far from a Nobel prize-winning revelation, but it was good practice to get a feel for how real science works. We observed something in nature, and we did an experiment to try and explain why that thing happened to be like that. We didn’t just look up an answer; we created one.

Want to see what a similar crustacean choice experiment looks like in an actual scientific journal? Check this out:
http://nature.berkeley.edu/classes/es196/projects/2011final/Panlasigui_2011.pdf

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