Trigoniulus corallinus, the rusty millipede (sometimes called the rusty red millipede), is a small, fast-breeding species that's become popular in bioactive setups. They're not a handling pet in the way giant millipedes are, but they're interesting in their own right and dead simple to keep.
What they look like
Adults are around 5-7 cm long, with a warm rust-brown to reddish colour that gives them their common name. They're on the slender side for a millipede and move noticeably faster than larger species. If you try to pick one up, it'll be halfway across your hand before you've finished the thought. Not aggressive, just quick.
Originally from Southeast Asia, T. corallinus has become pantropical, turning up in warm regions around the world where it's been accidentally introduced. In the hobby, they're widely available and usually inexpensive.
Enclosure
They don't need much space. A small to medium terrarium works fine for a group. Something around 30x20x20 cm will comfortably house a small colony, and you can go larger if you're building a bioactive vivarium where they'll be part of the cleanup crew.
A tight-fitting lid matters more than you'd expect. These millipedes are small enough to squeeze through surprisingly narrow gaps, and they're more inclined to explore the upper edges of the enclosure than larger species.
Substrate and environment
Standard millipede substrate applies: rotting deciduous hardwood, coco coir, organic topsoil, and leaf litter. No softwoods. Mix in some calcium (cuttlefish bone fragments, crushed eggshell). Depth of around 8-10 cm is enough for this species since they're much smaller than the giant species and don't need as much burrowing space.
Temperature: 22-26C suits them well. They're tropical, so don't let things drop below 18C for extended periods. Humidity: 70-80%, maintained by regular misting and a moisture-retentive substrate.
They appreciate plenty of leaf litter on the surface. Oak and beech leaves work well. In a bioactive setup, the leaf litter layer is both food and habitat for them.
Feeding
Same diet as other millipedes: decaying wood and leaves form the bulk of it. They'll eat cucumber, courgette, and mushroom pieces left on the substrate surface. Occasional banana. Keep a cuttlefish bone available for calcium.
In a bioactive vivarium, they largely feed themselves by processing the decaying organic matter in the setup. That's the whole point of having them there. They break down waste, dead leaves, and leftover food, cycling nutrients back into the substrate.
Breeding
This is where T. corallinus differs from larger millipede species. They breed readily in captivity and can build up numbers fairly quickly if conditions are right. Females lay eggs in the substrate, and the tiny pedelings emerge after a few weeks. Given warmth, humidity, and adequate food, a small group can become a sizeable colony within a year.
This makes them useful for several purposes. Bioactive vivarium seeding is the obvious one. But they're also a good species if you want to observe millipede reproduction and development without waiting years for results, the way you would with A. gigas.
Handling
Honestly, they're not really a handling species. They're small and fast, and the experience isn't particularly rewarding for either party. You can pick them up without any risk to yourself or the millipede, but they'll walk off your hand quickly and you'll spend more time chasing them than anything else.
If you want a millipede you can sit and hold, look at Archispirostreptus gigas or Epibolus pulchripes. T. corallinus is more of a "watch them do their thing" species.
In bioactive setups
This is where these millipedes really come into their own. They're one of the best invertebrate species for bioactive terrariums. Their job is breaking down organic waste: dead leaves, shed skin, leftover food, decaying plant roots. They process this material and their frass (droppings) enriches the substrate for live plants.
They coexist well with isopods and springtails, the other common bioactive cleanup species. Between the three groups, you get a fairly complete decomposition cycle. The millipedes handle the larger organic matter, the isopods work on slightly smaller stuff, and the springtails tackle mould and fungi.
A colony of T. corallinus in a well-maintained bioactive vivarium will largely look after itself. Keep the conditions right (warm, humid, plenty of leaf litter), and they'll persist and reproduce without much intervention.