Friday night in downtown Toronto I stepped out my front door to cars rushing past and the glow of streetlights. I was looking for something to photograph. I turned to my left, to a little planter box. Here, like everywhere else on the planet, there were interesting and beautiful creatures with jointed legs and exoskeletons. This is what I found underneath an old chunk of 2×4:
I thought I’d found a pill bug, with the delightful spiky symmetry and rows of yellow spots, but it wasn’t. Pill bugs are in the family Armadillidiidae, named for the trait they share with armadillos, the ability to roll into a ball when disturbed. This one just scurried away quickly. Instead, it was a common rough woodlouse (Porcellio scaber). You can recognize Porcellio scaber by their overall rough texture, the three lobes on their head, and two short appendages sticking out the back (called uropods). Normally they are gray or slightly bluish. This individual seems to be more colorful than usual.
This other individual has more typical coloration.
Woodlice and pill bugs are not insects but Isopods, a group of crustaceans. There are around 10,000 described species of isopods making them by far the most successful terrestrial crustaceans – most crustaceans reside in the ocean. About half of all isopod species are marine and half terrestrial, with a few living only in freshwater habitats. The isopods that live in and near our homes still hold evidence of their aquatic past. Appendages that served as gills in aquatic isopods evolved to be pseudolungs in terrestrial species. However, holes in the pseudolungs that allow for gas exchange cannot be closed making them very vulnerable to desiccation. That is why they stay in moist and dark places.
Rough woodlice (also known as rough sowbugs) feed on decaying organic matter, but also their own feces (coprophagy). Two hypotheses why they do this are: 1) to maintain copper in their system which is an important element in making haemocyanin (the protein that transports oxygen in circulatory systems of most invertebrates), and 2) to maintain the diversity and abundance of symbiotic bacteria that aid in digestion, especially of cellulose. Another biological waste fact, they excrete their nitrogenous waste as ammonia gas instead of urine. Possibly this serves as a defense against predators. Woodlice often huddle together in very tight spaces so it seems they must be careful not to turn their slumber party into a deadly gas chamber! Hopefully they have a strict ‘step outside to deposit your nitrogenous waste’ rule :) Lots more facts about these nifty animals here and here.
Porcellio scaber are native to Europe but they are very closely associated with humans and are now common all over the world. There are likely many in-and-around your house right now. I am glad I stopped to take a closer look. When was the last time you looked closely at those little animals you found and played with as a kid? Well, supposedly I am something of an adult now but and I learning to regain that relentless curiosity. It is a good way to spend a Friday night.