Rusty Armoured Millipede (Polydesmida sp.)

A flat-backed millipede looks built rather than grown. Each ring flares out at the sides into a keel, so the animal reads as a column of overlapping plates instead of a tube, and in this one the plates are a rusty brown, the colour behind its trade name, the Rusty Armoured Millipede.

What it is, and why the label says Polydesmida

It is sold in the UK as Polydesmus sp. 'Rusty', with Thailand given as its origin, and I have not kept that genus name. Polydesmus belongs to the northern temperate world, mostly Europe and the Mediterranean, with a single species known from northern Vietnam and no accepted record from Thailand. A rusty flat-back from Thailand is unlikely to be one. Its flat, keeled build points to the order Polydesmida, so I list it as Polydesmida sp. 'Rusty' until someone works out the genus. Beyond sharing that order, it is probably no close relation of the native British animal I sell as the tiny flat-backed millipede.

Appearance and size

Like every member of its order it has no eyes, and it navigates through its antennae, which are dense with sensory structures. The colour can catch you out at first. A flat-back fresh from a moult comes out pale, and its full colour builds over the following weeks, so a washed-out animal may simply have shed recently.

Size is an open question. No measurement of this animal has been published, so I have left length blank in the care panel rather than guess.

Care and set-up

Damp comes first. Keep the bed moist all the way down rather than sprayed on top, and aim for 80 to 90 per cent humidity. Lay 10cm or more of substrate, mixing flake soil with organic topsoil and plenty of white-rotted hardwood, then cover it with mixed leaf litter and a mat of live sphagnum moss, which holds moisture at the surface and gives them a humid layer to sit in. Coir does not belong in the mix: it keeps the bed wet and feeds nothing in it. Young flat-backs build little chambers to moult in, so once everything is in place, resist the urge to dig.

Keep them at 22 to 26°C. That band sits above what a British home manages through much of the year: the typical English home sits around 19°C while the heating is on, and even an average summer falls just short, so budget for a heat mat or heat cable run from a thermostat and fixed to a side wall, never underneath. Ventilate well enough that the air keeps moving. Like other flat-backs, this one very likely defends itself with a secretion that gives off a trace of hydrogen cyanide along with benzaldehyde, the almond smell you may notice. The cyanide is far too little to poison a keeper, but it can build up in a sealed container, so never shut them in an airtight box; wash your hands with soap once you have handled one, and keep the secretion away from your eyes.

Diet

The substrate is most of the menu: rotting hardwood and leaf litter, renewed as the colony eats its way through. Offer a slice of soft fruit or vegetable from time to time and a little fish flake on occasion, and take away whatever is left the next day. For calcium, a chunk of Malawi light limestone does the job. Steer clear of hydrated lime, the kind sold for building, which is caustic.

Breeding

Females lay their eggs in small chambers they build from soil and droppings, and the young hatch with only six legs, adding rings and legs as they moult. Flat-backs are generally short-lived. Most are thought to live for a year or two, and in the usual pattern for the order the adult matures, mates and dies in its final stage. I have found no account of this one being bred. Mine are wild-caught, so there is no knowing how old each one is, and with a life that short I would plan on keeping a group and letting it breed rather than expecting any single animal to be with you for years. A deep, undisturbed, wood-rich bed is the best chance you can give them.

Who the Rusty suits

This is a millipede for a keeper with a species or two behind them who likes the less familiar ones. Expect it to live mostly in the litter and moss; it is not one to handle often, and its care comes down to keeping a warm tub evenly damp. If you would like another flat-back from Southeast Asia beside it, the Pink Dragon belongs to the same order, and my guide to flat-backed millipedes explains what sets the whole order apart.

Each Rusty order goes out in a vented tub lined with damp moss, which then goes into a double-walled box; on cold days I add a heat pack. Dispatch runs Monday to Thursday. Every livestock order is protected by my live arrival guarantee, on Royal Mail Tracked 24 just as on Next Day.