Common Pillbug

Armadillidium vulgare is the most common terrestrial isopod in the temperate world. Despite living on land everywhere, pillbugs are not insects — they're crustaceans, descended from marine ancestors that crawled onto land approximately 350 million years ago. Pillbugs retain several aquatic adaptations: they breathe through gill-like 'pleopodal lungs' that must stay moist (which is why pillbugs are always found in damp places), they drink water through specialized tubes at the rear of the abdomen called 'uropods,' and they excrete ammonia gas directly through the body wall (most insects excrete uric acid). When threatened, the pillbug rolls into a defensive ball — the namesake 'roly-poly' behavior shared with armadillos, hence the genus name *Armadillidium*. Pillbugs are major decomposers in soil ecosystems, breaking down dead plant matter and recycling minerals. They have a unique ecological role: they actively concentrate heavy metals (cadmium, lead, copper, zinc) in their hepatopancreas tissues, sequestering them from the broader environment. This makes pillbugs widely used as bioindicators for soil heavy-metal contamination — biologists count and dissect pillbugs to measure soil pollution.