Siamese Glow Millipede (Benoitolus siamensis)

The name promises more than the darkness delivers, and I would rather be straight about that from the start. The Siamese Glow Millipede does not make its own light. Switch the lamp off and it is simply a dark millipede sitting in the substrate. Shine a UV torch on it, though, and the whole animal changes character: under a 365nm blacklight the shell answers with a soft, electric blue-green that traces every body ring. That is fluorescence rather than the true bioluminescence of a firefly or a glow-worm, and once you know how to trigger it, it is one of the best hidden features in the millipede world.

Benoitolus siamensis is a Southeast Asian member of the order Spirobolida, native to the forests and coastal edges of Thailand, and it travels the hobby under several names. You will see it listed as the Siamese Glow Millipede, the Glow in the Dark Millipede and occasionally the Glow-Worm Millipede. They are all the same species, and none of them light up on their own. The name is on the move as well: a 2026 study reassigned the animal to Pseudospirobolellus siamensis, so that is the current combination, though the databases and the whole trade still say Benoitolus and I am keeping that name on the page because it is what people search for.

In ordinary light it is an understated animal, a smooth, dark, cylindrical millipede that stays modest in size next to the African giants. I said here that I would tighten the size figure once I had something better than trade copy, and the same 2026 paper supplies it: adults of both sexes run about 5 to 6cm, males with 64 to 66 leg-bearing rings and females with 61 to 63. The 6 to 8cm this page used to give was too generous at the top by a clear margin. Like all millipedes they add rings and legs with each moult rather than arriving at full length.

Behaviour is where this species earns its place as a first millipede. It is slow, deliberate and mostly night-active, spending daylight tunnelling through the substrate and surfacing to graze after dark. It is comfortable in company, so a small group living together in one enclosure suits it well. When startled it curls into a flat coil rather than rolling into a tight ball, and it can release a defensive fluid that stains skin and irritates it if it is left on, and that burns an eye badly enough to need treating, so wash with soap after handling and before you touch your face. It will not bite.

Care is straightforward once you get the substrate right, because for a millipede the substrate is also the pantry. Give it a deep bed, at least as deep as an adult is long and ideally 15 to 20cm, built on decaying hardwood and leaf litter with plenty of white-rotted wood worked through it. That soft, rotting wood is not decoration; it is the bulk of the diet, and a deep layer lets the colony burrow, moult and feed in safety. Avoid softwoods, which do not agree with millipedes, and never stand the enclosure on a heat mat, since bottom heat dries the bed from below and bakes animals that live inside it. Room temperature is fine: aim for the low-to-mid twenties Celsius, roughly 20 to 26°C, keep the substrate damp and humid at around 75 to 85 percent, and allow a little airflow so it stays sweet rather than stagnant.

Alongside the substrate they will pick at soft fruit and vegetables in small amounts, and they need a steady source of calcium to reharden the exoskeleton after each moult, so keep cuttlebone or crushed shell within reach. One honest note on the glow: save the UV torch for the occasional viewing. Keeping these millipedes under a blacklight around the clock stresses them and is not what that fluorescence is for.

If the UV trick is what draws you in, the Siamese Glow sits naturally beside our Hawaiian Glow Millipede, which answers a blacklight the same way, or the more flamboyant Thai Rainbow Millipede if daylight colour is more your thing; you will find the full range on our millipedes for sale page.

A note on provenance: this is a Thai species, but the animals I send out are captive-bred in the UK rather than wild-caught. I do not breed this one here myself; it comes from UK breeders, which usually means hardier, better-settled stock than newly arrived wild-caught animals. They travel the same careful way regardless: a ventilated tub with damp sphagnum inside an insulated, double-walled box, dispatched Monday to Thursday by Royal Mail next-day delivery, with a heat pack tucked in when the weather turns cold, and every order covered by our live arrival guarantee. In more than twenty years of keeping reptiles and other exotics, I have found the understated animals hold your attention longest, and a plain dark millipede that turns electric under a torch is a hard one to beat.