Armadillidium granulatum is one of the more accessible Mediterranean Armadillidium species - large, hardy, and available in several attractive morphs. This guide covers their care requirements based on their actual biology and typical hobby practice in the UK.
About the Species
Armadillidium granulatum is a coastal Mediterranean species, found from Portugal and Spain along the French, Italian (Sardinia and Sicily included), Croatian, Greek and Turkish coasts to North Africa, typically living under stones near the shore. NOT tropical despite occasional misclassification. That stony, summer-dry shoreline informs everything about how to keep them.
Key biological points:
- Size: 16-17mm, up to 19mm, in Budde-Lund's 1885 measurements - one of the larger Armadillidium species; continental breeders quote up to 25mm, which no published measurement we have found supports
- Origin: Mediterranean and Atlantic-Iberian coasts, Portugal to Turkey and North Africa
- Behaviour: Conglobators (roll into a ball when disturbed)
- Reproduction: Sexual, not parthenogenetic. Males and females both required for breeding. Live young carried in marsupium (brood pouch)
- Gestation: Approximately 30 days
- Breeding rate: Moderate - slower than P. scaber or P. laevis but reliable in good conditions
- Lifespan: 2-3 years for adults
Available Morphs
Several selectively-bred colour morphs are available in the UK hobby:
- High Yellow - distinctive yellow spots on dark grey base. The most popular morph. Browse our A. granulatum High Yellow
- Orange - overall orange-tinted body. Browse our A. granulatum Orange
- Pearl - pearlescent white-cream colouration. Browse our A. granulatum Pearl
- Standard wild type - grey base with subtle markings. Browse our A. granulatum
Enclosure Setup
Container
10-litre minimum for a starter colony. Larger is better for breeding success. Plastic storage containers with secure lids work well - add ample ventilation.
Substrate
Standard Mediterranean Armadillidium substrate mix:
- 40-50% organic topsoil as the moisture-retaining base, not coir
- 20-30% organic topsoil or flake soil - our flake soil
- Crumbled decaying hardwood throughout - our shredded rotten wood
- Generous leaf litter on top - our leaf litter
- Small limestone pieces scattered through (calcium, and the kind of stone a shore-dwelling animal sits under)
Depth: 5-8cm minimum. Avoid peat moss (acidic, wrong for Mediterranean species which prefer neutral-to-alkaline).
Ventilation
Important. Mediterranean species need good air movement - they don't tolerate the high humidity stagnation that suits tropical species. Use mesh ventilation panels for cross-flow. Our screw-in air vents.
Hides and Structure
- Cork bark - essential
- Lotus pods - natural enclosed spaces
- Decaying wood pieces (also food)
- Limestone pieces optional aesthetic plus calcium
Calcium
Always-available cuttlebone on substrate - never crushed or powdered. Passive access; isopods consume as needed. See our calcium supplementation article.
Environmental Conditions
Temperature
18-22°C - standard UK room temperature is fine. Don't need supplemental heating in most UK homes. Mediterranean species evolved with seasonal temperature variation and tolerate moderate ranges well. Heat mats or lamps are unnecessary and can actually stress them.
If your home is consistently cool (under 16°C in winter), a low-wattage heat mat on the side of the enclosure, on a thermostat and never underneath it, provides a thermal gradient. Never heat lamps for isopods.
Humidity
50-80% across the enclosure, from about 50% at the drier end to 80% in the damp corner. Mediterranean species need DRIER conditions than premium Cubaris. Both ends of the enclosure should differ:
- Wetter end: lightly misted substrate, sphagnum moss patches
- Drier end: rarely misted, more open substrate, closer to natural Mediterranean conditions
Mist the wetter end every few days; let the drier end mostly stay drier. This allows the colony to self-regulate - a critical Mediterranean species adaptation.
Feeding
Foundation Diet
- Leaf litter - the dietary foundation. Oak, beech, hornbeam, maple - see our leaves article
- Decaying hardwood - both food and habitat
- Flake soil - background nutrition
- Calcium - always-available cuttlebone
Fresh Vegetables (1-2 times weekly)
- Courgette/zucchini
- Carrot
- Cucumber
- Sweet potato
- Butternut squash
- Apple slices (occasionally)
Protein Supplements (Weekly Maximum)
Use established hobby options:
- Fish flakes - the standard. See our fish flakes article
- Dried shrimp / bloodworm - clean and easy. See our shrimp article
- Repashy Bug Burger - commercial isopod formulation
Avoid: cooked chicken or fish (attract mites and mould rapidly), excessive protein supplementation. For broader feeding context see our protein feeding article.
Breeding
A. granulatum is sexually reproducing. Both males and females required for breeding - there's no parthenogenesis in this species (despite some sources claiming otherwise).
Once mated, females carry developing embryos in their marsupium (brood pouch) for approximately 30 days before releasing live mancae (baby isopods). With good husbandry, colonies produce broods regularly.
Breeding conditions:
- Stable temperature (18-22°C)
- A humidity gradient (drier end available)
- Adequate hides and refuges (especially important for vulnerable freshly-moulted individuals)
- Varied diet with adequate protein
- Consistent calcium provision
- Avoid frequent disturbance during breeding phases
Mancae develop within the substrate and emerge gradually. Don't worry if you don't see them immediately - they hide in substrate while small.
Common Mistakes
Treating as Tropical Species
The most common mistake. Keepers used to Cubaris husbandry maintain A. granulatum at tropical conditions - too humid, too warm. This stresses them and reduces breeding success.
Sealed Enclosures
Mediterranean species need ventilation. Sealed containers cause respiratory stress and colony decline.
Inadequate Calcium
Calcium dusting (sprinkling powder) doesn't work for isopods. Always-available cuttlebone is the hobby's standard method.
Heat Lamps
Heat lamps dry out the enclosure and stress isopods. Never use them. Heat mats on thermostats only if needed for cool homes.
Over-Misting
Mediterranean species don't want soggy substrate. Light misting at one end, drier conditions at the other.
Their Place in a Collection
A. granulatum is an excellent intermediate species:
- Larger and more visually striking than basic UK natives
- Less demanding than premium Cubaris
- Multiple morph options available
- Reliable breeders with good husbandry
- Conglobate display behaviour adds interest
Best started after basic species (Powder Orange, Dairy Cow, P. scaber morphs) have given you husbandry experience. Their slightly more specific needs (humidity gradient, ventilation) make them a useful intermediate stepping stone.
Companion Articles
For broader Armadillidium guidance see our Armadillidium collection. For setup essentials browse our accessories collection. For comprehensive setup guidance see our first isopods guide. For temperature considerations see our cold tolerance article.
For current stock browse our isopods collection.
Simple to keep once you understand they're Mediterranean species, not tropical. Get the humidity gradient and ventilation right and they'll thrive for years.
Mancae Development
Young (mancae) emerge from the marsupium as miniature versions of adults. They:
- Have only 6 leg-bearing segments initially (the 7th pair grows in over the first three moults)
- Are independent immediately on release
- Develop through successive moults rather than metamorphosis
- Reach adult size over several months depending on conditions
No "neoteny" involved - they're not insects, they don't undergo metamorphosis, and there's no juvenile stage that bypasses adult form.
Difficulty Assessment
Intermediate-level isopods:
- Easier than Cubaris - more forgiving of variable conditions
- More demanding than Powder species - need a humidity gradient and ventilation
- Good first Armadillidium - accessible without being basic
- Recommend 3-6 months hobby experience before attempting
Common Problems
Colony Decline
Most often traces to humidity issues:
- Too humid - the most common mistake. A Cubaris-style box, damp throughout at 75%+, causes Mediterranean species to struggle
- Too dry - also problematic; need humid gradient
- Solution - establish a gradient, ensure cross-flow ventilation, let substrate dry partially between mistings
Slow Breeding
Several possible causes:
- Insufficient calcium for egg production
- Inadequate dietary variety
- Temperature consistently below 18°C
- Recent colony stress
- Colony still establishing (give 3-6 months)
Mould Issues
Indicates excessive humidity or poor ventilation. Adjust ventilation rather than removing substrate. The granular texture of A. granulatum sometimes masks mould; check carefully if you suspect issues.
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