Armadillidium vulgare is probably the most recognised isopod on the planet. It is the one that rolls into a ball. Everyone has poked one as a child and watched it curl up. That conglobation reflex is a defensive behaviour specific to the genus Armadillidium and a few other genera. Not all isopods can do it. Porcellio species, for instance, cannot. They just leg it.
As a pet, A. vulgare is hardy, tolerant, and available in some genuinely attractive colour morphs. It is a little slower to breed than Porcellio scaber, but it makes up for that by being tougher and more handleable.
Quick facts
- Order: Isopoda, Suborder: Oniscidea
- Family: Armadillidiidae
- Adult size: 12-18mm
- Lifespan: 2-4 years
- Origin: Mediterranean region (now cosmopolitan)
- Difficulty: beginner
Appearance and conglobation
Wild-type A. vulgare is grey to dark grey, sometimes with lighter mottling along the edges of each segment. The body is strongly convex (domed), which is what allows it to roll into a tight ball with the legs and soft ventral surface fully enclosed. The outer surface of the rolled-up isopod is the hardened dorsal exoskeleton, which provides genuine protection against small predators and desiccation.
Conglobation is not just a party trick. It is an effective defence that reduces water loss and presents a hard surface to anything trying to eat it. In captivity it mostly just means they curl up when you disturb them, which makes them very easy to pick up and move around.
How it differs from Porcellio
Armadillidium species are generally more drought-tolerant than Porcellio. A. vulgare copes with drier conditions that would stress a P. scaber, though it still needs access to moisture. It is also slower-moving and slower to breed. Where a P. scaber colony might double in a few months, A. vulgare builds up more gradually.
The body shape is the obvious difference. Armadillidium is convex and smooth-edged when viewed from above. Porcellio is flatter with more prominent lateral extensions on each segment. Once you have seen both side by side, you will not confuse them again.
Enclosure
Same basic setup as any isopod. A ventilated plastic tub, 5-8cm of substrate, leaf litter, cork bark, and a piece of cuttlefish bone. Because A. vulgare tolerates drier conditions, the moisture gradient can lean slightly drier than for tropical species. The damp end still needs to be damp, but the dry end can be properly dry without causing problems.
Ventilation can be slightly more generous than for humidity-dependent species. A. vulgare does well with more airflow, which also reduces mould. A mesh-topped enclosure or a lid with larger ventilation holes works well.
Substrate
The standard mix works fine: organic topsoil, coco coir, sphagnum moss, leaf litter, and a bit of sand. A. vulgare appreciates limestone or chalk in the substrate, which provides both calcium and the mildly alkaline conditions it seems to prefer. A handful of crushed limestone mixed through the substrate is a nice addition for this species.
Temperature and humidity
Temperature: 16-24C. Perfectly happy at UK room temperature year-round. It copes with brief cold snaps better than most tropical species, reflecting its Mediterranean and temperate European origins.
Humidity: 50-70% on the damp side. It does not need the 70-85% that tropical species require. If the damp end is consistently moist and there is a cuttlefish bone for calcium, A. vulgare is very forgiving. Overwatering is more of a risk with this species than underwatering, simply because keepers tend to mist more than necessary.
Diet
Leaf litter (oak, beech) as the staple. Vegetable scraps weekly: carrot, sweet potato, courgette. Protein weekly in small amounts. Calcium always available. Exactly the same feeding approach as other common species. A. vulgare is not a fussy eater.
This species does well with dried leaves that are slightly more decayed. Partially decomposed leaves with visible fungal growth on them are prime food. The isopods eat the fungi along with the leaf tissue.
Colour morphs
The "Magic Potion" morph is the star of A. vulgare in the hobby. It produces individuals with bright orange and grey/blue patterning. Each animal looks different, with the pattern varying from mostly orange to mostly grey. A colony of Magic Potion in a display enclosure is genuinely eye-catching.
T-positive albino lines exist, producing pale yellow or orange animals with reduced dark pigment. Various other colour lines are being developed. Prices for morphs are higher than wild-type but have come down as availability has increased.
As with all morphs, keep them separate from wild-type and from other morphs of the same species to prevent reversion.
Breeding
Slower than Porcellio species. Brood sizes of 15-30 mancae are typical. Expect 2-3 broods per year per female under good conditions. The colony builds gradually rather than explosively. This is fine. It just means you need to be patient in the early months and resist the urge to conclude the colony is failing just because you are not drowning in babies.
Warmer temperatures (upper end of the 16-24C range) speed up breeding. Good calcium availability helps females produce healthy broods. These are the two levers you can pull if you want faster growth.
As a bioactive cleanup crew
A. vulgare is less commonly used in bioactive setups than P. scaber because it breeds more slowly and the population recovers more slowly if the main animal eats some of them. The hard, domed exoskeleton also makes it less suitable as a feeder item for small reptiles compared to the softer-bodied Porcellio species. It works, but it is not the optimal choice for this purpose.
Handling
This is one of the best isopod species for handling. It rolls into a ball rather than running, so you can scoop it up and it sits in your palm. It unrolls after a minute or so and will walk around on your hand. Children find this particularly entertaining, and it is a genuinely good species for young keepers as a first pet invertebrate. Just wash hands before and after, and avoid dropping them.