Pillbugs vs. Sowbugs. . .Which Do You Prefer?

Ms. Eckert's classroom is the home of many organisms.  There is Savannah (our leopard gecko), Clem (our albino axolotl), our many pillbugs as well as sowbugs, and many tiny microorganisms that we cannot see!  In the beginning of the year, there was a lab conducted by our biology class to observe the behavior of the species Armadillidium, commonly referred to as pillbugs.  The purpose was to evaluate what types of environments the pillbugs preferred to reside in.

Drawing copyright © 1997 R. Brusca.

Pillbugs are classified in the order of Isopoda which include crustaceans that range in various shapes and sizes.  Isopods are commonly mistaken as insects due to the fact that they are small and live in the ground, however, they are terrestrial crustaceans.  As in most crustaceans, the isopod body is divided into three distinct regions of the head (cephalon), thorax, and abdomen (pleon).  The first segment of the thorax is fused to the head.  There are usually seven free segments called pereonites of the thorax that make up the pereon.  They also have compound eyes, two pairs of antennae, and four sets of jaws.  Isopods also are found in marine and terrestrial habitats as well, but most of these creatures live in water.  Common marine crustaceans include lobster, crab, krill, shrimp, and barnacles.  Crustaceans respirate through gills that are located where the legs attached to the thorax. 

Before actually starting the experiment, the biology class compared the differences between two terrestrial crustaceans, pillbugs to sowbugs.  Pillbugs and Sowbugs are recognized by their wingless, slate­ grey colored, round­-back, bodies that have segments which resemble armored plates.  Their oval bodies are convex above but flat underneath.  They also have seven pairs of legs and two pairs of antennae, although one pair is barely visible.  Sowbugs, the species Porcellionidae, are typically larger than pillbugs and also have two tail-like appendages that jet out at the rear end of the body.  Since pillbugs do not have these appendages, it allows them to roll up into a tight ball when disturbed - hence the name "rolly-polies."

 Can you identify which ones are sowbugs and which ones are pillbugs?

Pillbugs and sowbugs are found in moist environments, commonly outdoors.  Occasionally, they will end up in buildings but have no fear if you find them in your house!  They may be found in large numbers but these bugs do not bite, sting, or transmit diseases.  Indoor environments are often too dry so the pillbugs and sowbugs will die soon after coming inside.  Both species play a role in the cycling of nutrients as they feed mainly on decaying organic matter.  They can only thrive in environments of high moisture such as damp areas under objects.  Around buildings and playgrounds are common areas to find them.  Do you remember digging in the ground when you were younger and finding rolly-pollies in the soil? I hope that I wasn't the only kid who did that.

I personally like pillbugs and because they are a lot calmer than sowbugs.  When I let a pillbug walk across my hand, it takes its time to crawl and I get a chance to see its physical characteristics.  I also think its really cool that pillbugs can curl up into balls - c'mon they even got a good name for themselves!  Sowbugs are a bit bigger and more aggressive when traveling.  They like to move quickly and are more frantic.  When I placed a sowbug in my hand, it kept trying to run away and eventually just fell off my hand. 

Here is one of the class's pillbugs! (left: curled up, right: crawling)

Now let me show you a sowbug (left: crawling OFF my hand, right: back in its habitat)

So although pillbugs and sowbugs are pretty similar. . .which do you prefer?