This week in BIOL 326 we set out to test something that any eight-year-old with a penchant for bugs could tell you. If you are looking for wood bugs (also known as isopods, wood louse, pill bugs, or sow bugs), where do you find them? The answer is under things, or more specifically in our study, under logs! We found that wood bugs were significantly more abundant underneath logs than on top of them; shocking, I know.
But we didn’t stop there, after all we have grown up at least a little bit since being eight. We collected some of the isopods and took them back to the lab in order to try to determine why these wood bugs were so much more abundant under logs. We tested three separate hypotheses, that this habitat choice was being made based on light, moisture, or temperature. We tested each of these hypotheses by placing isopods in petri dishes or aluminum foil boats where the isopods could choose between two different habitat types: light or dark, wet or dry, and cold or warm.
Using these choice experiments we found that these isopods were responding to all three of the variables we tested. They preferred darkness to light, wet to dry, and cold to warm; all of which parallel the differences we would expect between the top and bottom of logs!
Isopods belong to a group of mostly marine animals known as the Crustaceans (think shrimps, crabs, and lobsters), so those isopods that live on land – such as the wood bugs – can be in danger of drying out. Not only do wood bugs have to worry about losing water through evaporation from their skin, but they breathe using gills, which only work if they are moist. So being in dry, warm environments can not only make wood bugs dehydrated but it can make it hard for them to breathe! It therefore makes sense that wood bugs prefer living in places like underneath logs, where it is cooler and more humid than the surrounding area. This preference for moist areas is thought to be one of many adaptations to land used by terrestrial isopods to conserve water.
Another possible explanation for this habitat preference is that wood bugs are safer from their predators when they are hiding under logs. Predators such as birds and spiders are probably less able to catch wood bugs when they are hidden under logs, although we didn’t test this hypothesis in this lab. Maybe next time?
To learn more about wood bugs and countless other creepy-crawlies you can check out the incredible Victoria Bug Zoo; or if that’s too far away, get in touch with your own inner child and just start flipping logs!