Love for the Isopod

The roly-poly is common, but also special, almost like it has a magical power to enthrall and interest children. Other creatures that live under rocks and logs, which we affectionately refer to as the underworld, can cause more of a fear response in children. I’ve seen them scream and run from spiders, centipedes, and even earthworms. I have rarely seen that reaction to roly-polies.

To start off, what are roly-polies? Well, they go by a variety of names, and they are not all the same. The group of animals roly-polies belong to is called isopods. These are terrestrial crustaceans. Most crustaceans we are familiar with are ocean dwellers: lobsters, crabs, and shrimp. And while on the surface our friendly roly-polies look nothing like those other crustaceans, they are remarkably similar.

All crustaceans, roly-polies included, have jointed legs, a hard exoskeleton like insects and arachnids, segmented bodies, and gills. Yes, our terrestrial isopod buddies breathe through gills on the underside of their bodies. This is why they are almost always found in damp and dark environments under rocks and logs. Keeping their gills moist is crucial for their survival.

Now, I’ve been using the term roly-poly, which is usually what the kids call them, but that name is not always accurate. Roly-poly refers to one group of woodlice, or terrestrial isopods, that can roll up in defense. Like an armadillo or hedgehog, these little guys will roll into a tight ball, almost a perfect sphere, to keep their more delicate and sensitive undersides, including gills and legs, safe within the armor of their exoskeleton.

Photo via flickr, Jeff Tome
Many isopods are found in groups, preferring to live in large colonies.

Not all isopods can do this, in fact, most of the isopods we find here at Audubon or in schoolyards cannot roll up. These non-roly-polies have a few different names. I have polled my coworkers here in the ACNC education office and we have developed a highly official hierarchy of isopod names. Potato bugs can refer to any land isopods, whether they can roll or not. Roly-polies and pillbugs have the ability to roll. The isopods that can’t roll we call sowbugs. These are, of course, entirely colloquial terms and your results may vary.

Potato bugs of all sorts play an important role in the environment. They are a major decomposer, helping to break dead organic matter, mostly plant bits like leaves, seeds, and stems. They are also an important food source themselves for many small predators like spiders, toads, centipedes, and small mammals like shrews.

While we may be used to our terrestrial potato bug friends, it is important to note that there are aquatic isopods as well. The most impressive of which is the aptly named Giant Isopod. This superficially looks very similar to the terrestrial ones with one major difference: its size. These gentle giants can get to be large, up to 20 inches long. But if this makes you uncomfortable, don’t worry. Your chance of meeting one is very low. The large size is an example of a phenomenon called deep-sea gigantism, where deep ocean dwellers become much larger than their shallow ocean or terrestrial counterparts. If you want to find one of these giant isopods, you will need to take an excursion to the depths of the ocean.

So next time you are flipping over logs and rocks, appreciate the isopod. Feel their legs tickle as they crawl over your hand (just make sure you put it back), watch them scurry into little holes or roll up into a tight ball. Think of their little gills, hard at work keeping them alive in an environment they weren’t entirely designed for. They are cool little creatures and we shouldn’t take them for granted.