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.

In ordinary light it is an understated animal, a smooth, dark, cylindrical millipede that stays modest in size next to the African giants. Adults tend to reach somewhere around 6 to 8cm, and like all millipedes they add rings and legs with each moult rather than arriving at full length. Treat that size as a guide rather than a promise; I will tighten the figure here once I have measured my own adults.

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 mild defensive fluid, so a quick hand-wash before and after handling is sensible. 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 26C, 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 imports. I do not breed this one here myself; it comes from UK breeders, which usually means hardier, better-settled stock than freshly imported 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, isopods and other inverts, 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.