Which White Isopod Is Which? A UK Identification Guide

The trade borrowed its albino vocabulary from snake keeping, and the words did not survive the journey. A "T+ Albino" isopod is not tyrosinase-positive in any demonstrated sense, because tyrosinase is a melanin enzyme and melanin is not what gives a woodlouse its colour. The names are worth keeping, since they are what customers search and what every vendor prints. The explanation underneath them is the part that needs replacing.

The short version

White isopods arrive at white by three separate routes, and identifying one is mostly a matter of working out which route you are looking at.

• Pigment that was never made. The animal cannot build its normal body pigment, so it is pale throughout.
• A layer sitting on top of the cuticle. A microscopic surface coating scatters light and reads as frost.
• A species that was never coloured. Some isopods are unpigmented as their ordinary wild state, not as a bred line.

There is a fourth group that is not white in the strict sense at all: patterned animals carrying white markings on a fully pigmented body.

White because the pigment was never made

Isopod body colour is built from ommochromes, pigments assembled from the amino acid tryptophan. Those belong to a different chemical family altogether from melanin, which is the pigment doing the work in a snake or a mouse.

Hasegawa and colleagues (1999) found that the albino strain of Armadillidium vulgare has extremely low activity of tryptophan 2,3-dioxygenase, an enzyme near the start of the ommochrome pathway, while two enzymes further along were unchanged. Jovović, Figon and Bilandžija reached the same conclusion independently in 2022 working on cave isopods: albinism blocked at the beginning of the same pathway.

Isopods do make melanin. Bilandžija and colleagues (2017) showed where it goes: wound repair, hardening the mouthparts and the tips of the appendages, and walling off parasites. None of that is body colour. So when a listing tells you melanin gives wild vulgare its grey base colour, it is wrong, and you will find that claim on more than one shop page.

Animals in this group include the T+ Albino and T- Albino vulgare, Whiteout and Ghost Porcellio scaber, the leucistic-carrying werneri and the Albino Rubber Ducky. What they have in common is reduced or absent pigment, distributed through the whole animal, and inherited.

What the T names actually tell you

Nothing mechanical. In snakes, T stands for tyrosinase and separates two kinds of albinism. No tyrosinase mechanism has ever been demonstrated in any isopod, and because melanin is not the pigment in question, there is no coherent sense in which a woodlouse can be tyrosinase-negative. "T+ Albino" appears across eight or more independent vendors, so the name has earned its place. "T- Albino" is fringe by comparison, roughly two. Read both as trade labels for particular bred lines.

White because of something sitting on top

The powder isopods work by a completely different mechanism. Vittori and Gantar (2020) examined the frosted bloom on Porcellionides and found microscopic spheres on the cuticle surface, built from proteins and glycoproteins, and in their words without detectable amounts of lipids.

Two things follow from that. It is not pigment, so a Powder White is not an albino. And it is not wax, which is the word the hobby reaches for almost every time. The spheres are laid down early in premoult around branching extensions of the epidermal cells, so the layer is rebuilt at every moult.

The measured effect is water repellency. Cuticle carrying the spheres is more hydrophobic than cuticle with the spheres experimentally removed.

Powder White, Powder Orange and Powder Blue are all one species, Porcellionides pruinosus, carrying the same structural layer over different underlying colour. Their care is identical across the three and lives in the Powder Orange and Blue guide.

Two claims get made about the bloom that nobody has published: that it rubs off with handling, and what colour the animal is underneath it. Neither has been measured, and I would not repeat either.

White that is a pattern, not a loss

Milky Way, White Panda King, White Side and Milk Back all carry white as a marking on an otherwise pigmented animal. The pigment machinery is intact and simply distributed differently. None of them is an albino line, and none will behave like one in a breeding project.

The practical tell is edges. A depigmented animal is pale everywhere and pale all the way through. A patterned animal has a boundary somewhere on it, and the boundary is usually crisp enough to see without magnification.

Buying from a photograph makes this harder than it needs to be, because most listing shots are taken from directly above. If you are unsure, ask whether the pale colour carries onto the antennae, the legs and the underside. A loss of pigment does not stop at the edge of the area a camera happens to show.

A species that was never coloured to begin with

Dwarf Whites are Trichorhina tomentosa, and they are the group most often filed in the wrong drawer. They are not a bred albino line of some coloured ancestor. Unpigmented is what the species is.

They run 3 to 5mm, small enough that most keepers meet them as a cleanup crew instead of a display animal. No males are known, so reproduction is understood to be parthenogenetic, though there has never been a dedicated experimental demonstration of it, which is why understood is the honest word and proven is not. Full husbandry sits in the Dwarf White care guide.

Three things worth not repeating

Pale morphs are not weaker. No published work links colour morph to vigour, lifespan or fertility in any isopod. The nearest evidence points mildly the other way: Durand and colleagues (2018) found that inbreeding in A. vulgare cost some neonatal mortality but had no detected effect on the growth or survival of the offspring that lived.

A line going patchy is not genetic drift. Drift is a specific population process. A recessive line throwing mixed young is segregation plus whatever you selected for, or stock that has been contaminated. Both are husbandry problems with husbandry answers, and the mechanism is covered in the genetics and morphs article.

White eyes are not a published diagnostic. The expectation is reasonable, since ommochromes screen the crustacean eye as well as colouring the body, and keepers use it as a shortcut all the time. No isopod paper states it. Treat it as a hint, never as proof.

Common questions

Is a Powder White an albino?

No. Its white comes from a structural layer on the surface of the cuticle, not from missing pigment. Underneath that layer the pigment pathway is working normally.

Are Dwarf Whites an albino Trichorhina?

No. There is no pigmented wild form for them to be an albino of. The species is unpigmented in the wild.

Why do two shops sell the same white animal under different names?

Because most of these names are trade labels attached to particular bred lines, not descriptions of a mechanism. Two lines can look alike and carry different names, and one name can cover more than one line.

Will a white morph breed true?

That depends entirely on which line you have bought, and it is a question about inheritance instead of about colour. Ask the seller what the parents were and how many generations the line has been running.

Do white isopods need different care?

No. Care follows the species. A white vulgare wants what any vulgare wants, and a Dwarf White wants what Trichorhina wants. The full range sits under isopods for sale.