There are quite a few types of wood lice, but the Armadillidiidae family of wood louse is unique in that it can roll up into a ball, or conglobate (pronounced “con-glow-bate”). Many nonscientists have acknowledged this unique trait with their own descriptive names: pill bug, roly poly, basketball bug or curly bug.
I grew up calling these critters potato bugs, but other common names in the United States are chuckie pig, armadillo bug and doodlebug. Because the bugs are found worldwide, they have many names throughout the world, including bed pisser in the Netherlands, bench biter in Denmark, cellar bug in Germany, cheeselog in the UK and fat pig in Ireland.
Whatever name you call them, you may not know that most pill bugs are native to the Mediterranean. In New England, the best-known species, Armadillidium vulgare, came here accidentally in the early 1800s in lumber, ornamental plants or ships’ ballast (early 19th-century ships used soil and rocks as ballast).
What is the purpose of a pill bug? In ecosystems, organisms are classified by what they eat. We all know what carnivores and herbivores eat. Pill bugs are decomposers. They munch on dead matter — mostly rotting wood, decaying leaves, fallen fruit. This process breaks down large pieces of plant material into smaller pieces, so that still smaller decomposers like bacteria and fungi can continue the recycling process, putting nutrients, like carbon, nitrogen, and phosphorous, back into the soil. Without decomposers, dead leaves and wood would pile up around you. So think of pill bugs as fertilizer producers for your garden.
And while we call them bugs, pill bugs are not insects. Insects have six legs, but pill bugs have 14. Pill bugs are in fact a type of crustacean.
Like other crustaceans, pill bugs have a hard exoskeleton, a segmented body and two pairs of antennae. Crabs, lobsters, shrimp and barnacles are all crustaceans, but they are found in the ocean. Pill bugs, while terrestrial, are not that well-suited to land. They dry out easily and, like other crustaceans, they do not have lungs. Instead, they breathe through gills.
To keep from drying out, they avoid the sun and come out mostly at night, but you can find them in the day if you turn over rocks or logs or dig in damp soil. If you turn a pill bug upside down, you will see two white spots beside the abdomen. These spots contain branched tubes that evolved from aquatic gills. The gills transfer oxygen from the air to the pill bug’s blood. The gills only work when they are damp. If the air is too dry, the pill bug suffocates.
Most organisms, including humans, produce waste high in ammonia, which is excreted in urine. But ammonia and other waste fluids in pill bugs escape as gases through pores in the exoskeleton. They do not need to rid their body of moisture to remove ammonia. In other words, they do not pee. This is important for staying hydrated in a terrestrial world.
Pill bugs also eat their own solid waste. Of course, this behavior, too, has a scientific name: coprophagy. Scientists think this behavior evolved to help pill bugs retain copper, which is hard to find in the environment. Pill bugs use copper to transport oxygen in the blood, unlike humans, who use iron. One thing copper changes is the color of a pill bug’s blood. Oxygenation (when copper ions attach to oxygen molecules) causes pill bug blood to change color from light gray to blue. In humans, oxygenation of iron causes blood to change from dark red to bright red. (FYI, human blood is never blue, even though veins near the surface of your skin look blue because of the way the skin scatters light, reflecting blue wavelengths while absorbing red.
If you’ve heard that pill bugs clean heavy metals from the soil and thought it was an urban legend, in fact, they can store heavy metals in their bodies without being poisoned. A digestive gland (the hepatopancreas) crystallizes toxins into granules that are stored in the midgut. You might be familiar with the hepatopancreas from lobsters and crabs, where we know it as the greenish paste diners call the tomalley (and are advised to eat sparingly). Just like in pill bugs, it stores contaminants like mercury, PCBs and other toxins. Because pill bugs can sequester heavy metals and other toxins, they can live in contaminated soil that other organisms cannot. Although the hepatopancreas is small (about five percent of a pill bug by weight), it stores 80 percent of its lead and copper.
So, if pill bugs are related to yummy lobsters and crabs, how does a pill bug taste? In his 1885 tome Why Not Eat Insects? Vincent M. Holt writes that the flavor of pill bugs is “remarkable akin to their sea cousins.” He goes on the tell how to cook them: Collect a quantity of the finest wood-lice to be found (no difficult task, as they swarm under the bark of every rotten tree), and drop them into boiling water, which will kill them instantly. . . . At the same time put into a saucepan a quarter of a pound of fresh butter, a teaspoonful of flour, a small glass of water, a little milk, some pepper and salt, and place it on the stove. As soon as the sauce is thick, take it off and put in the wood-lice. This is an excellent sauce for fish.
The taste of pill bugs is perhaps what gives rise to still another name for this creature: wood shrimp. And while some foragers claim pill bugs taste like shrimp, others claim they taste like dirt. Since my urban soil is probably full of lead or other contaminants, I think I will leave them alone to do what they do best: decompose the detritus in my garden and yard.
A stronger
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