Siamese Glow Millipede (Benoitolus siamensis)

The name promises more than the darkness delivers, and I would rather be straight about that from the start. I have found no record of the Siamese Glow Millipede making light of its own. 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, an endemic Thai species recorded from the Samae San islands off Sattahip, in Chonburi Province on the Gulf of Thailand, and it travels the hobby as the Siamese Glow Millipede or the Glow in the Dark Millipede, two names for the one species. The name is on the move as well: a 2026 study reassigned the animal to Pseudospirobolellus siamensis, so that is the current combination, and when I checked in October 2026, MilliBase, the world catalogue of millipede names, listed it as the accepted name. The trade and the main index of GBIF, the Global Biodiversity Information Facility, still say Benoitolus, and I am keeping that name on the page because it is what people search for. My Siamese Glow millipede care guide covers the name change and the animal's care in full.

In ordinary light it is an understated animal, a smooth, cylindrical millipede, dark grey with orange bands and orange-tan legs, 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 and deliberate, and by sellers' accounts it climbs as well as burrows. 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 simple 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. Aim for the low-to-mid twenties Celsius, roughly 20 to 26°C. A British room reaches that in summer but sits below it through the colder months, so fix a heat mat or cable on a thermostat to the side wall for those months. Keep the substrate damp and humid at around 75 to 85 per cent, 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 limestone, cuttlebone or crushed shell within reach. One word of caution on the glow: save the UV torch for the occasional viewing. I have found no study of what long exposure to ultraviolet does to millipedes, so I would not leave a blacklight on over the tub.

If the UV trick is what draws you in, the Siamese Glow sits naturally beside the 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 the 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 Tracked 24, or Special Delivery Guaranteed by 1pm if you choose Next Day at checkout, with a heat pack tucked in when the weather turns cold, and every order covered by the 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 grey-and-orange millipede that turns electric under a torch is a hard one to beat.