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10 Cool Facts About Pillbugs

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Though we call them bugs, pillbugs are really crustaceans like shrimp and crabs.

Though we call them bugs, pillbugs are really crustaceans like shrimp and crabs.

Photo: Joseph Berger, Bugwood.org

A pillbug goes by many names -– roly poly, wood louse, armadillo bug, potato bug – but whatever you call it, it's a fascinating creature. These ten facts about pillbugs will give you a new respect for the tiny tank living beneath your flower pots.

1. Pillbugs are crustaceans, not insects.
Though they're often associated with insects and are referred to as "bugs," pillbugs actually belong to the subphylum Crustacea. They're much more closely related to shrimp and crayfish than to any kind of insect.

2. Pillbugs breathe through gills.
Like their marine cousins, terrestrial pillbugs use gill-like structures to exchange gases. They require moist environments to breathe, but cannot survive being submerged in water.

3. A juvenile pillbug molts in two sections.
Like all arthropods, pillbugs grow by molting a hard exoskeleton. But pillbugs don't shed their cuticle all at once. First, the back half of its exoskeleton splits away and slides off. A few days later, the pillbug sheds the front section. If you find a pillbug that's gray or brown on one end, and pink on the other, it's in the middle of molting.

4. Pillbug mothers carry their eggs in a pouch.
Like crabs and other crustaceans, pillbugs tote their eggs around with them. Overlapping thoracic plates form a special pouch, called a marsupium, on the pillbug's underside. Upon hatching, the tiny juvenile pillbugs remain in the pouch for several days before leaving to explore the world on their own.

5. Pillbugs don't urinate.
Most animals must convert their wastes, which are high in ammonia, into urea before it can be excreted from the body. But pillbugs have an amazing ability to tolerate ammonia gas, which they can pass directly through their exoskeleton. So, there's no need for pillbugs to urinate.

6. A pillbug can drink with its anus.
Though pillbugs do drink the old-fashioned way – with their mouthparts – they can also take in water through their rear ends. Special tube-shaped structures called uropods can wick water up when needed.

7. Pillbugs curl into tight balls when threatened.
Most kids have poked a pillbug to watch it roll up into a tight ball. In fact, many people call them roly polies for just this reason. Its ability to curl up distinguishes the pillbug from another close relative, the sowbug.

8. Pillbugs eat their own poop.
Yes indeed, pillbugs munch on lots of feces, including their own. Each time a pillbug poops, it loses a little copper, an essential element it needs to live. In order to recycle this precious resource, the pillbug will consume its own poop, a practice known as coprophagy.

9. Sick pillbugs turn bright blue.
Like other animals, pillbugs can contract viral infections. If you find a pillbug that looks bright blue or purple, it's a sign of an iridovirus. Reflected light from the virus causes the cyan color.

10. A pillbug's blood is blue.
Many crustaceans, pillbugs included, have hemocyanin in their blood. Unlike hemoglobin, which contains iron, hemocyanin contains copper ions. When oxygenated, pillbug blood appears blue.

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