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Backyard Crustaceans

We’ve really got to hand it to arthropods. Numbering over 1 million species, arthropods (insects, crustaceans and spiders) make up over 80% of classified living and fossilized species- and that’s only accounting for known species. As a compost enthusiast, arthropods become increasingly endearing, as many of them are detritvores (species that feed on decomposing organic matter). Between facilitating nutrient cycles and adapting to a huge diversity of environments, arthropods definitely deserve our gratitude and admiration! Now, if you spend time composting or gardening, you may have (1) a similar respect for the insects helping to maintain your soil, pollinate your plants, and chow on pests (just to name a few services) or (2) a distinct sense of fear and disgust for any living thing with more than four legs. Whether you are a member of the former or the latter group, it can be exciting to gain a little more insight into these fascinating creatures. A great place to start is proper identification: some common backyard arthropods are not insects at all, but terrestrial crustaceans! These garden crustaceans are more closely related to crayfish, crabs and lobsters than to beetles and centipedes!

WOODLICE, including SOW BUGS and PILL BUGS are members of the order Isopoda, forming the suborder Oniscidea- the only crustaceans that have adapted to living entirely on land. Despite their terrestrial lifestyles, woodlice have retained gill-like breathing structures (pleopod lungs and pseudotrachea) that allow them to thrive in high-moisture habitats (like inside your compost bin or underneath your potted plants!) There are thousands of species of woodlice, with the notable pill bug belonging to its own genus, Armadillidium.  So how do you distinguish a pill bug from a sow bug? Pill bugs have jointed exoskeletons that allow them to roll into a sphere, while sow bugs’ more rigid exoskeleton disallows this function. Also useful for visual identification, sow bugs are larger in size and, like most other crustaceans, have two small tail-like appendages (uropods) at the back of the abdomen. Here are a few characteristics of these garden crustaceans that are not immediately observable:

  • Committed Partners: Many species of woodlice are monogamous, with both partners sharing parental and housekeeping responsibilities.
  • Gender Benders: Female woodlice can reproduce asexually. Male woodlice sometimes change sex if infected with Wolbachia- a hormone disrupting bacteria.
  • Creative Waste Managers: Woodlice do not urinate, as they can pass ammonia gas through their exoskeletons (so there’s no excuse not to pick them up!)

Now that you’ll be spending more time examining your local woodlice population, you may notice some colorful variations on the typical slate-colored specimen:

  • Orange coloring in woodlice is an extremely rare genetic variation found largely among Porcellio scaber (but has also been spotted in others, such as Philoscia muscorum). Their striking hue is less advantageous for camouflage than the dark grey coloration of their more common counterparts.

  • Blue or purple coloring in woodlice is not a genetic variation, but rather, a physical reaction to an iridovirus that creates dense accumulations of crystalline structures in infected tissues. These structures produce an intense blue or purple coloration in individuals with advanced stages of the disease. Unfortunately, these little guys are quickly on their way to becoming compost.

  • Two-toned woodlice are in the midst of moulting their exoskeletons, which occurs every couple months in two phases (back half moults first, front half moults a few days later). The two-part process is believed to confer lower vulnerability to predation during moulting.

Who knew that the cousins of plankton and prawns were so well adapted to your garden space? Be sure to say hello the next time you see them hard at work!