Hangin’ with Isopods!

Have you ever rolled over a decomposing log and seen hoards of little plated bugs scurrying everywhere, trying to seek out shelter again? These bugs are typically referred to as ‘pill-bugs”, ‘sow bugs’ or ‘wood lice’, and are a common type of terrestrial isopod found under logs, sticks, leaves and stumps around Vancouver.

A terrestrial isopod (or, 'wood bug'.  Image source: wikipedia

A terrestrial isopod (or, ‘wood bug’. Image source: wikipedia

There are three primary species in the region, Armadillidium vulgare, Oniscus asellus and Porcellio scaber, but Oniscus is the most common. We set out to determine habitat preference in Oniscus (henceforth also referred to as ‘wood bugs’) by doing what ecologists do best – getting our hands dirty!

Our plan was to head out to Pacific Spirit park, at the University of British Columbia to determine habitat preference of Oniscus on top of or under logs, then bring some back for additional laboratory experiments. We set out to count the abundance of Oniscus on top of each log, we measured each log , then flipped it over and measured the abundance underneath while checking the temperature on top and underneath. All the while, we collected as many Oniscus as possible in ziplock bags.

We brought the wood bugs back to the university and carried out several laboratory experiments involving temperature, moisture and light. After collecting some class data, and carrying out some statistics we were able to determine that in the park, the wood bugs preferred the more cool, under-side of the logs. This was confirmed by our laboratory experiments, which showed that wood bugs preferred cooler temperatures, and also more moist conditions. Even though Oniscus are terrestrial organisms, they still breath through gills, so they need the moisture in order to keep their gills damp to be able to breathe!


Typical looking cluster of woodbugs on the underside of a log. Image source: thenaturalmuse.blogspot.com

Interestingly, we used some historical data of rainfall to determine that isopod abundance seems to decrease as average rainfall increased. This was a surprising result, as we assumed that Oniscus would do better under more moist conditions, however, there are certainly many more ecological factors that could be involved in isopod abundance in the forest.   Needless to say, we were still able to infer a lot about the behavioural habitat preferences in these species in just a few hours, making the afternoon well worth the work.


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