Armadillidium vulgare

About this species

Armadillidium vulgare, commonly known as the common pill bug or roly-poly, is probably the isopod you already know. They turn up in gardens everywhere. Native to Europe, it has been introduced to every other continent (except Antarctica) and thrives in gardens, woodlands, and grasslands across temperate regions.

The main trait that distinguishes Armadillidium from Porcellio and other genera is its ability to conglobate, rolling into a complete, tight ball when disturbed. This defensive behaviour is where the common name "pill bug" comes from, and it is a reliable way to tell Armadillidium species apart from lookalikes.

Enclosure

A. vulgare does well in any well-ventilated plastic or glass enclosure. A starter colony of 20 individuals is comfortable in a container with a 20×15 cm footprint. Good ventilation is important. Cross-ventilation through side vents and the lid helps prevent stagnant, overly humid conditions that this species dislikes.

Provide cork bark, dried leaves, and a piece of cuttlebone or limestone as permanent fixtures. A small clay hide or piece of bark on the slightly damp side gives them a retreat when needed.

Substrate

A. vulgare appreciates a calcareous substrate that supports their relatively high calcium needs. A good mix is:

• 60% coco coir
• 20% organic topsoil
• 10% fine sand for drainage
• 10% crushed limestone or cuttlebone powder

Keep a moisture gradient, with one corner consistently damp, with the rest of the enclosure allowed to stay relatively dry. A. vulgare prefers drier conditions than many other isopod species and will avoid waterlogged areas. A depth of 5–8 cm is sufficient. Top with dried oak or beech leaves for both shelter and food.

Feeding

A. vulgare is an unfussy detritivore. A balanced diet includes:

• Dried leaves (oak, beech, nettle), the staple of their diet
• Vegetables: cucumber, courgette, carrot, sweet potato
• Cuttlefish bone for calcium, needed for healthy moults and their calcareous exoskeleton
• Occasional protein: dried shrimp or fish flakes once a week

Calcium supplementation is particularly important for Armadillidium species, whose thicker, more heavily mineralised shells demand a steady supply. Cuttlefish bone can stay in the enclosure permanently. They will graze on it as needed. Remove uneaten fresh food after 48 hours to prevent mould.

Breeding

A. vulgare breeds readily in captivity once a colony is settled. Females carry eggs in a brood pouch (marsupium) on their underside, and mancae (young) emerge as miniature versions of the adults. At stable temperatures of 18–24°C, females will begin reproducing within a few weeks of being introduced to a good setup.

This species breeds a little more slowly than fast-reproducing Porcellio species, but colonies build steadily over time. Avoid disturbing the substrate during the first couple of months. A colony started with 20 individuals can grow to 50–80 within six to twelve months under good conditions.