High Yellow Spotted Giant Isopods (Armadillidium gestroi) are one of the most visually striking species in the hobby. With their bold yellow spots and patches scattered across a dark purplish-grey body, they're genuinely eye-catching - the kind of isopod that makes people stop and look twice.
Native to southwestern France (particularly the Aquitaine region) and parts of Italy, these isopods are found naturally along coastlines and in areas with limestone, sandstone, and granite substrates. They're one of the larger Armadillidium species, reaching up to 2cm, and have confident, active personalities once established.
Armadillidium gestroi shares similarities with the popular Clown Isopod (Armadillidium klugii) - both Mediterranean species with spotted patterns thought to serve as a defence mechanism. Like all Armadillidium, they can roll into a tight protective ball when threatened.
A Glimpse
Origin: France (Aquitaine region), Italy
Scientific Name: Armadillidium gestroi
Difficulty Level: Easy
Size: Up to 20mm (one of the largest Armadillidium)
Temperature: 20-26°C (21-24°C optimal)
Humidity: 60-80%
Rarity: Low to Medium
An Overview
Armadillidium gestroi has earned its place as a hobby favourite through a combination of stunning appearance, manageable care requirements, and rewarding behaviour. The "High Yellow" line has been selectively bred to enhance the vibrant yellow colouration, and the results speak for themselves.
These are larger isopods than many keepers expect - adults can reach nearly 2cm in length with a substantial, rounded body shape. Their colouration ranges from bright acid-yellow to pumpkin orange spots on a dark grey-purple base, with individual variation meaning each isopod has its own unique pattern.
One thing to note: A. gestroi can be slow to establish initially. Juveniles take their time growing to maturity, and new colonies may seem quiet for the first few months. Patience is key. Once established, however, they produce impressively large broods - reportedly over 100 offspring per clutch in some cases - so your patience will be rewarded.
They're more confident and active than many isopod species. Rather than hiding constantly, established colonies will be out exploring during the day, making them excellent display animals.
Basic Care
Armadillidium gestroi are considered easy to care for once you understand their preferences. They're hardy and forgiving, making them suitable for beginners who want something more visually impressive than standard species.
Unlike many Armadillidium that prefer drier conditions with high ventilation, A. gestroi actually favours slightly higher humidity than its relatives. They do best with moderate humidity (60-80%) and appreciate a moisture gradient - one section kept damp while the rest stays drier.
Ventilation is still important but should be more moderate than for species like Zebra Isopods. Fewer ventilation holes will help maintain the humidity levels these isopods prefer.
Temperature should be maintained between 20-26°C, with 21-24°C being optimal. They're tolerant of temperature fluctuations but avoid extremes - both excessive heat and cold can be lethal.
Provide plenty of hiding spots using cork bark, wood pieces, and leaf litter. They appreciate having options on both the moist and dry sides of their enclosure.
A shoebox-sized container (6-8 quart) is suitable for a starter colony. Given their slow initial growth, you'll have plenty of time to upgrade as the colony expands.
Adding springtails to the enclosure is highly recommended. They'll help manage any mould that develops in the higher-humidity environment and work alongside your isopods as part of a balanced cleanup crew.
Feeding
Armadillidium gestroi are detritivores, primarily consuming decaying organic matter. Their natural diet in the wild includes leaf litter, rotting wood, lichens, grasses, and other decomposing plant material.
Primary foods (should always be available):
Hardwood leaf litter (oak, beech) - the foundation of their diet
Rotting white wood
Sphagnum moss
Bark pieces
Supplementary foods (offered 1-2 times weekly):
Fresh vegetables - carrots, courgette, sweet potato, pumpkin, cucumber
Fruits - apple, banana (sparingly, as these spoil quickly)
Protein sources - fish flakes, freeze-dried shrimp, dried mealworms
Calcium supplementation is essential for healthy moulting and reproduction. Provide constant access to:
Cuttlefish bone
Crushed eggshells
Crushed oyster shell
Limestone pieces (mimics their natural habitat)
A. gestroi originate from areas rich in limestone, so calcium is particularly important for this species. They'll actively seek it out.
Be careful not to overfeed fresh foods. In the higher humidity environment these isopods prefer, uneaten food can quickly develop mould and disrupt the enclosure balance. Offer only what can be consumed within 24 hours and remove any leftovers promptly. Place protein foods on the drier side of the enclosure where they're less likely to spoil.
Appearance and Behaviour
The defining feature of A. gestroi is their spectacular colouration. Bright yellow to orange spots and patches are scattered across a dark purplish-grey or brown base colour. The contrast is striking and genuinely impressive in person - photos don't always do them justice.
Adults reach approximately 18-20mm in length, making them one of the largest Armadillidium species available. They have the characteristic rounded, pill-shaped body of the genus with a smooth, calcified exoskeleton. Their antennae are relatively long and slender.
Colouration can vary between individuals, ranging from vivid acid-yellow to warmer pumpkin-orange tones. As juveniles mature, their colours may darken slightly, with the base colour becoming more pronounced. The "High Yellow" line has been bred to maximise the yellow pigmentation.
Behaviourally, these are confident isopods. Once established and comfortable in their environment, they'll be active and visible during the day rather than hiding constantly. They may be shy initially (especially as juveniles in a new enclosure) but become bolder as the colony settles.
Like all Armadillidium, they can conglobate - rolling into a complete ball when threatened. This defence mechanism, combined with their spotted pattern (thought to mimic warning colouration), helps protect them from predators.
They're social and do well in groups with no aggression between individuals. Colonies will often cluster together in favourite hiding spots.
Habitat
A plastic storage container (6-8 quart minimum) or glass terrarium (5-10 gallons) works well for a starter colony. As these isopods are slow-growing initially, you'll have time to assess space needs before upgrading.
Ventilation should be moderate - enough for airflow but not so much that humidity drops too low. A. gestroi prefer slightly higher humidity than many Armadillidium species, so fewer ventilation holes than you might use for Zebra Isopods is appropriate. Cover any holes with fine mesh to prevent escapes.
Temperature should be maintained at 20-26°C. Avoid temperature extremes in either direction.
Humidity should follow a gradient approach. Keep roughly one-third to one-half of the enclosure moist (with damp sphagnum moss and substrate), while the rest stays drier. Aim for overall humidity of 60-80%.
Hiding spots are essential and should be provided on both the moist and dry sides of the enclosure. Cork bark is ideal - it provides shelter and doubles as a long-term food source. Lotus pods, coconut halves, and pieces of rotting wood also work well.
Springtails are highly recommended as tank mates. They'll help control mould in the humid environment and won't compete with or harm your isopods.
Avoid placing the enclosure in direct sunlight, which can cause dangerous temperature spikes and rapid humidity loss.
Substrate Mix
The right substrate mix is crucial for A. gestroi, providing food, maintaining humidity, and supporting the beneficial bacteria that help break down organic matter.
Base substrate options:
Coconut coir
Peat moss
Pesticide-free topsoil
ABG mix or similar bioactive substrate
Mix in:
Rotting white wood pieces
Decaying hardwood leaves
Earthworm castings
Charcoal (helps with drainage and filtration)
Calcium supplements (limestone pieces are particularly appropriate given their natural habitat)
Layer on top:
Generous covering of leaf litter (essential food source and hiding spots)
Patches of sphagnum moss (on the moist side)
Cork bark pieces for hides
Lichens (if available - these isopods enjoy them)
Substrate depth should be at least 5-7cm to allow for burrowing. Maintain a moisture gradient within the substrate - the area under moss patches should stay consistently damp while other areas can be drier.
The substrate should never be waterlogged but also shouldn't be allowed to dry out completely. These isopods breathe through gills and require access to moisture for respiration.
Breeding
Armadillidium gestroi will breed readily once established, though patience is required during the initial settling-in period. Colonies can take several months to really get going, particularly if you start with juveniles.
Sub-adults will begin breeding before reaching full size, but the slower growth rate of this species means you'll wait longer for reproduction to begin compared to faster-growing species.
The good news: once breeding does commence, A. gestroi produce impressively large broods. Some sources report over 100 mancae (baby isopods) per clutch, so established colonies can grow rapidly.
For optimal breeding success, provide stable conditions with moderate humidity (60-80%), temperatures around 21-24°C, abundant leaf litter, plenty of hiding spots, and consistent calcium availability.
Females carry eggs in a brood pouch (marsupium) and give birth to live young. The tiny mancae can be raised alongside adults without any issues - no separation is needed.
Juveniles grow slowly compared to many species, taking several months to reach maturity. This is normal for A. gestroi, so don't worry if growth seems gradual.
