### Identification At first glance, *Actaecia thomsoni*—often called the Beach Pillbug—looks like a tiny, animated grain of quartz. Measuring a mere 4–5mm, this isopod is perfectly oval and highly convex. Its coloration is its greatest defense: a pale, translucent creamy-white or light grey, often speckled with minute darker dots that mimic the texture of coastal sand. To distinguish it from common garden woodlice, look at the eyes—*A. thomsoni* possesses large, dark, multi-faceted eyes that stand out against its pale "armor." When threatened, it performs a seamless "conglobation," rolling into a tight, spherical bead that is almost impossible for a predator to grip.
### Habitat & Range This specialist is a creature of the supralittoral zone—the high-tide "splash zone" of sandy beaches. While found across various New Zealand coastlines, they are most abundant on fine-grained, sheltered beaches. You won't find them in the forest; they are tethered to the driftline (the wrack line), where the ocean deposits its bounty. They spend their days buried several centimeters deep in the cool, moist sand beneath logs or mats of decaying seaweed to avoid the desiccating sun.
### Behaviour Observed at night with a headlamp, *A. thomsoni* is surprisingly athletic. They emerge from the sand to scavenge, scurrying with impressive speed across the dunes. They are solitary foragers but often congregate where food is plentiful. Their most remarkable trait is their "tidal clock"; even when removed from the beach, they maintain a rhythmic activity pattern synchronized with the local tides to ensure they aren't caught out in the open during a high-tide surge.
### Diet As essential beach recyclers, these isopods are detritivores. They feed primarily on "sea wrack"—decaying kelp, seagrass, and other organic debris washed ashore. By shredding this tough material, they accelerate the nutrient cycle, turning rotting seaweed into fertilizer for dune-stabilizing plants.
### Fascinating Fact Despite living their entire lives on the beach, *Actaecia thomsoni* cannot swim! If they are accidentally swept into the surf, they will quickly drown. To prevent this, they possess a highly "tuned" sense of humidity and vibration, allowing them to migrate up or down the beach to stay in the "Goldilocks zone"—damp enough to breathe through their pleopods (gills), but dry enough to stay out of the waves.