Dwarf White Isopods (Trichorhina tomentosa)

There is no such thing as a male dwarf white. Every animal in the culture is female, every one of them produces young without ever meeting a mate, and the practical upshot is that you cannot get the sex ratio wrong, cannot buy a group of the wrong sex, and cannot fail to breed them for any reason other than neglect. It is the closest thing the hobby has to a self-running culture.

Introduction

These are Trichorhina tomentosa, sold as Dwarf White Isopods or Tropical White Isopods, and they are the workhorse of the bioactive world rather than a display animal. They come from tropical Central and South America, they are tiny at 2 to 4 mm, effectively blind, and they spend nearly all their time down in the substrate where you will scarcely see them. What they lack in presence they make up for in usefulness: almost every serious bioactive setup has a colony of these ticking away underneath it, and almost every dart frog keeper uses them as food.

Appearance

Small, pale and downy. The body is a plain white to off-white with a fine felted surface texture, which is where the species name comes from, tomentosa meaning downy. Worth clearing up a persistent confusion at this point: dwarf whites are white, not blue. The Powder Blue isopod is a different species entirely, Porcellionides pruinosus, and the two get mixed up constantly in listings and care sheets. If yours look blue-grey, you have Powder Blues.

Care

Warm, damp and left alone. They want tropical conditions, which for most UK homes means a little gentle heat for part of the year, and a consistently moist substrate that never dries out, since drying is the one thing that reliably kills a culture. Ventilation still matters, so damp rather than waterlogged, with airflow enough to keep mould honest. They need very little space: a small tub with a few mesh-covered holes does the job, and the mesh needs to be fine, because at 2 mm these animals will find any gap. Underneath, give them a nutritious base of flake soil, white-rotted hardwood and organic topsoil topped with leaf litter, since they eat their substrate as it breaks down. Skip both coco coir and peat as the foundation, the first because it feeds nothing and the second because it is too acidic. Our flake soil and the botanicals in our accessories range cover the mix, and our substrate guide has the full recipe. A little cuttlebone helps moulting, though as a small, lightly armoured species they are far less calcium-hungry than the big Porcellio and Cubaris.

Diet

Leaf litter and decaying hardwood do nearly all of it, and they will graze the harmless surface mould that appears on damp organic matter, which is a large part of why they clean so well. A pinch of fish flake or a scrap of vegetable now and then keeps a growing colony fed, removed after a day or two. That is the whole of it.

Breeding

Effortless, by design. Parthenogenesis means every individual is a breeding female that clones herself, so numbers climb steeply given nothing more than warmth, moisture and food. There is no pairing to arrange, no ratio to balance and no waiting for a colony to sex out. A healthy culture will outgrow its tub, which is exactly what you want from something you intend to crop from.

Who is this for?

Three people, mainly. The dart frog, mourning gecko or small amphibian keeper who wants a live feeder that renews itself indefinitely and is the right size for froglets. The bioactive keeper who needs a micro cleanup crew for a small or heavily planted enclosure where a larger isopod would be clumsy, and who will get the best of it by running them alongside springtails, the orange ones especially. And the complete beginner who wants a first culture that is genuinely hard to kill. The one keeper they will disappoint is anyone after something to look at, since you will rarely see them. If you want visible cleanup, the Dairy Cow does the same job in plain sight. Everything else is in our isopod range, and there is more detail in our dwarf white care guide.

Cultures go out captive-bred and well established, covered by our live arrival guarantee and packed with moss and substrate in a double-walled box. Posting runs Monday to Thursday on Royal Mail next day before 1pm.