Granulatum High Yellow Isopods (Armadillidium)

The figure you will see everywhere for this species, ours included, is 25mm. We cannot find a source for it.

The measured figure we can find is Budde-Lund's, from 1885: adults 16 to 17mm, the largest 19mm. That is still large for the genus, which was always the truthful form of the selling point. A 22.8mm maximum circulates online, credited to a 2019 paper on the species' young. That paper's summary reports only the head widths of the young in their first three stages, about 0.5 to 1.2mm, and we have not been able to read the rest, so we cannot confirm that it measures any adult.

The yellow

Standard granulatum carry yellow dots that range from barely there to bright. This stock sits at the bold end of that range: more spots, denser, and a stronger yellow against the grey. Under a torch the effect is good, and it holds through to adulthood instead of fading as the animals grow.

One clarification on the name. High Yellow is a description, not a registered line. The same words get used loosely across several unrelated species in the reptile and invertebrate trade. The name stays because it is how the animal reached us and how you will find it elsewhere, not because it marks out a pedigree.

Mediterranean, not tropical

This is where most new keepers go wrong with the species. It wants a gradient and real airflow, not a sealed humid box. Persistent wet is the single condition this otherwise forgiving animal will not put up with, and it accounts for more losses than cold ever does. Avoid sustained extremes of temperature in either direction. Damp one end, let the other run drier, ventilation across the lid. Room temperature in a British house suits them year round with no heating at all.

Give 8cm of substrate on a topsoil base that has never seen pesticide, with grit or crushed shell worked through, a deep leaf layer, and flat bark for cover. They aggregate under it in heaps, which is normal and a good sign. Cover any ventilation holes with fine mesh; they are better climbers than they look.

Feeding and breeding

Decayed leaves and soft wood carry the diet. Keep cuttlebone available permanently, since a species this heavily armoured gets through calcium, and offer protein weekly. Do not overfeed: surplus food in the damp end grows mould and draws pests, so clear the leftovers inside a couple of days. Magnolia leaves hold their shape longer than oak and give the surface structure they graze over.

They breed early and often. Females frequently begin producing before they reach full size, which is ordinary across Armadillidium, so a group that still looks half grown may already be building numbers under the litter.

Range

Worth being precise, because our pages have tended to lead with Spain. The species is Mediterranean rather than Iberian, with records spanning Italy and Morocco as well as Spain, and coastal populations associated with dune and salt-tolerant vegetation.

The rest of the granulatum

The standard form is the cheaper way in and identical to keep. Three further selections of the same species sit alongside it. Orange and White Pearl take the warm and pale ends respectively, and Citrus Ghost sits between them. If you want a patterned Mediterranean instead of a spotted one, Zebra is the obvious comparison, and closer in size than the old figures suggested.

Our full Armadillidium granulatum care guide goes deeper on the species, from substrate and the humidity gradient to feeding and breeding, and it covers the High Yellow alongside the other morphs.

They leave on damp moss inside a punched tub, that tub sleeved into a second carton, shipped Monday to Thursday by Royal Mail, Next Day or Tracked 24 as chosen at checkout. We raise the count by a fifth above your order, and guarantee the animals land alive. Problems reported to us on the day of arrival get put right, no argument.