The Siamese Glow Millipede is a slim, orange-ringed Thai millipede named for the blue-green glow sellers report under an ultraviolet torch, though I have found no record of it making light of its own. The trade calls it Benoitolus siamensis, but a study published in July 2026 moved it to another genus, so its accepted name is now Pseudospirobolellus siamensis. Care is simple once the bed is right: a deep, damp substrate of flake soil, white-rotted hardwood and organic topsoil under leaf litter, 20 to 26°C, a little airflow, calcium always on offer and, through the colder months, a heat mat or heat cable on a thermostat, on the side of the tub, never underneath.
The name, and where it comes from
The specimen it was named from was collected in October 1916 by C. Boden Kloss on Koh Samae San, an island off Sattahip at the southern tip of Chonburi Province, on the Gulf of Thailand. Carl Attems described it in 1936 as Cyclothyrophorus siamensis, and it was later moved to Benoitolus. You will also see it sold as the Glow in the Dark Millipede.
In July 2026 Piyatida Pimvichai, Brigitte Segers, Karin Breugelmans and Thierry Backeljau moved it again, in a paper in the journal Animals. They examined fresh specimens from Koh Samae San and neighbouring Koh Chuang, and two mitochondrial genes placed the animal in Pseudospirobolellus, a genus of the Southeast Asian family Pseudospirobolellidae. The males' gonopods, the modified legs used in mating, fit that genus too once the 1936 description was reinterpreted. The paper calls it an endemic Thai species, and the specimens it lists come from those two islands, the fresh ones from 7 and 9 metres above sea level. I found no habitat note in its account of this species; sellers say it lives near beaches. Pimvichai also led the 2018 paper that named the animal in my Thai Rainbow Millipede care guide.
When I checked in October 2026, MilliBase, the world catalogue of millipede names, listed Pseudospirobolellus siamensis as the accepted name, while the main index of GBIF, the Global Biodiversity Information Facility, still filed it under Benoitolus. I use both names because people still search for the old one.
The glow: fluorescence, not bioluminescence
As I put it on the listing, "Switch the lamp off and it is simply a dark millipede sitting in the substrate." The glow needs ultraviolet. Under a 365nm blacklight, in the listing's words, "the shell answers with a soft, electric blue-green that traces every body ring." Another seller calls the colour electric blue, and a keeper has posted photographs of adults and young glowing together. That is fluorescence: the cuticle absorbs ultraviolet, invisible to the human eye, and gives it back as visible light.
Many millipedes fluoresce, though not all. In a 2017 imaging study using 350nm ultraviolet, Paul Marek found the strongest glow in the flat-backed order Polydesmida and recorded a bright blue from Spirobolida, the order this animal belongs to. He wrote that the role of fluorescence in millipedes "is uncertain and has not been empirically evaluated", and I have found no study of fluorescence in this species itself.
True bioluminescence is rare in millipedes. The best-known case is Motyxia, blind flat-backed millipedes from the mountains of California, whose glow a 2011 field study found works as a warning to predators. Keep a UV torch for short looks rather than leaving a blacklight on over the tub; I have found no study of what long exposure to ultraviolet does to millipedes.
Appearance and size
The 2026 paper gives adults of both sexes as about 5 to 6cm long and about 4mm across, the females slightly thicker. Males carry 64 to 66 leg-bearing rings and females 61 to 63, and the young add rings and legs at each moult. The 50 to 60mm in my care panel comes from that paper, which describes the living animal as dark grey, with the antennae, legs, the edge of the collar behind the head, the rear band of every ring and the tip of the tail light orange.
That pattern tells it apart from the Hawaiian Glow Millipede, which is sold as a Spirobolellus, a genus in a different family of the same order. The Hawaiian Glow is about 20 to 25mm long and banded black and white, while an adult Siamese Glow is two to three times that length and ringed in orange.
Setting up the enclosure
A small group can share one enclosure. Two seller pages, worded almost identically, describe the animal as living on trees in the wild, resting in branch forks packed with humus and leaves, and one suggests a terrarium of at least 20 x 20 x 30cm for its small size and its urge to climb. So give it height as well as depth, with a few bark flats leaned against the sides.
Make the bed at least as deep as an adult is long, ideally 15 to 20cm, because this is where it feeds and moults. Build it from flake soil, white-rotted hardwood and organic topsoil, with leaf litter on top; the Asian leaf mix I sell, gathered in Thailand and Vietnam, is a nod to its home, though ordinary broadleaf litter works too. Leave coir out, since it holds moisture but is not food for a substrate-eater, and use hardwood only, never pine or other softwood.
Expect animals to vanish for a while: one seller reports that it goes deep into the substrate for about a week to moult. Leave it alone when it does, because a millipede dug up mid-moult is at real risk; my guide to how millipede moulting works explains why.
Temperature and humidity
Aim for 20 to 26°C, the band in my care panel. At Sattahip, the district its islands belong to, the weather station's monthly means run from 26.3 to 29.9°C, all above the top of that band, and sellers' figures reach 28°C, so the upper half of the band is closer to home. English homes average about 19°C through the heating season, so for the colder months fit a heat mat or heat cable on a thermostat, on the side of the tub, never underneath: heat from below dries the bed and warms the layer the animals retreat into to moult. In summer a warm room may be enough, but check with a thermometer.
The panel gives 75 to 85 per cent humidity, and Sattahip averages about 77 per cent across the year. Keep the substrate damp to the squeeze rather than wet, water the bed itself when it starts to dry, and allow a little airflow so it stays fresh rather than stale.
Diet and calcium
For a millipede the substrate is the food. White-rotted hardwood and leaf litter are the staple, so top up the litter as it goes down. Alongside that they will pick at soft fruit and vegetables in small amounts, and one seller adds greens, moss, lichen and fish flakes. Take away anything uneaten before it moulds.
Keep calcium on offer at all times. Millipedes build calcium salts into the exoskeleton and rebuild it at every moult, so leave a piece of cuttlebone, or some crushed limestone or shell, on the surface. Most millipedes eat their cast skin, so leave a moult where it lies.
Breeding
It does breed in captivity: mine are captive-bred, though I do not breed this one myself. Beyond that, I have found no published account of its breeding, so what follows comes from the trade. One seller calls it moderately prolific and says that in the wild it lays its eggs in those humus-filled branch forks, where the young spend their early life. In a tub, leave the young with the adults in a deep, undisturbed bed, since in most millipedes the eggs and smallest young develop hidden in the substrate, where digging breaks them open. If nothing seems to be happening, why your millipedes may not be breeding works through the usual causes.
Handling and the defensive fluid
It cannot bite or sting, and you can let it walk across a flat hand. When startled it curls into a flat coil and may release a defensive fluid. I have found no analysis of this species' own secretion, but a 2025 study of a Thai relative in the same family, Coxobolellus saratani, found six quinones, led by a benzoquinone, and two phenols among its ingredients. Benzoquinones are the typical defence of spirobolid millipedes.
On skin the fluid stains and irritates if it is left on; in an eye it is a chemical burn that needs treating. Blindness is possible but rare, according to medical references, so rinse any secretion out of an eye and get it looked at promptly. Wash your hands with soap after handling and before you touch your face, and supervise children closely: seven of the eight patients in a published series of eye cases were children of seven and under. Are millipedes dangerous? covers the evidence in full.
Who it suits
My care panel rates it Easy, and I think it makes a good first millipede: small, content in a modest tub and undemanding once the bed is right. It suits anyone who wants an animal to watch by torchlight, or a keeper short of space who would rather not house a giant.
Frequently Asked Questions
Do Siamese glow millipedes actually glow?
Under ultraviolet light, yes. I have found no record of them making light of their own, but under a UV torch they fluoresce, blue-green as I describe it on the listing and electric blue to another seller; sellers specify 365nm. That is fluorescence, not the bioluminescence of a glow-worm or a firefly.
How big do Siamese glow millipedes get?
About 5 to 6cm long and roughly 4mm thick as adults, according to the 2026 redescription. The 50 to 60mm in my care panel comes from that paper.
What is Benoitolus siamensis called now?
Pseudospirobolellus siamensis. A July 2026 paper in the journal Animals moved it on DNA and gonopod evidence, and MilliBase now lists that as the accepted name. The trade and GBIF's main index still use Benoitolus, so you will see both.
Are Siamese glow millipedes poisonous?
They are not venomous, since they cannot bite or sting, but their defensive fluid is a chemical irritant. It stains and irritates skin if it is left on and is a chemical burn in an eye, so wash your hands with soap after handling, keep your hands away from your face and supervise children closely.
How long do Siamese glow millipedes live?
One seller gives two to three years. I have found no published lifespan for this species, so treat that as a single seller's figure.
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