Selenobrachys

Selenobrachys is a small genus of Old World tarantulas in the family Theraphosidae, native to the Philippines. It was first established in 1999 by Günter Schmidt to accommodate Selenobrachys philippinus from Negros Island, a bright orange terrestrial species that quickly became popular in the hobby.

In 2012, a major revision of Asian tarantulas treated Selenobrachys as a junior synonym of the genus Orphnaecus, so S. philippinus was referred to for years as Orphnaecus philippinus in both the scientific literature and the pet trade.

New morphological and DNA-based work by Acuña and colleagues in 2025 showed that Selenobrachys is actually distinct from Orphnaecus. Their ZooKeys study formally restored Selenobrachys as a valid genus and described a second species, Selenobrachys ustromsupasius, from Romblon Province. As of this revision, the genus Selenobrachys contains two recognized species—S. philippinus and S. ustromsupasius—both endemic to the Philippines, with S. philippinus remaining the type and best-known representative.

Selenobrachys ustromsupasius

Common name: Romblon Black Tarantula

Origin: Endemic to Romblon Island, Romblon Province, Philippines. This species is currently only known from low-elevation localities around Brgy. Tambac on Romblon Island.

Lifestyle: Old World, fossorial / obligate burrower. In nature it lives in burrows and retreats in roadside embankments, crevices of metamorphosed limestone (marble) outcrops, and piles of coconut husks, often in human-modified areas.

Adult size: Medium–large tarantula. Adult females are reported to reach around 4.5–6 in (11–15 cm) diagonal leg span.

Growth rate: Not formally studied, but based on keeper experience and comparison with its close relative Selenobrachys philippinus, it is considered a moderate to fast grower when kept warm and well fed. (You could phrase this as “medium to fast growth rate” on the site.)

Temperament: A typical defensive Old World burrower: very fast and reclusive, preferring to bolt into its burrow, but capable of strong threat postures and a painful bite if provoked. Best treated as a display species for experienced keepers; not suitable for handling.

Color & appearance: A brown to dark brown, sometimes almost black tarantula with a robust body and long, slender legs. Fresh molts can show warmer brown or subtle pinkish tones on the legs, while older individuals tend to look deep chocolate-brown to nearly black—hence the “Romblon Black Tarantula” name.

Species History

Selenobrachys ustromsupasius is a newly described Philippine tarantula and the second species in the genus Selenobrachys. It was formally named and described in March 2025 by Acuña and colleagues in a ZooKeys paper that also revalidated the genus Selenobrachys as distinct from Orphnaecus using both morphology and DNA data.

The species is endemic to Romblon Island in the central Philippines, where it occurs in roadside embankments, marble (metamorphosed limestone) outcrops and crevices, and piles of coconut husks—showing a strong association with disturbed, human-influenced habitats. In the hobby it was known informally as Selenobrachys sp. “Romblon pink” before its formal description.

The name “ustromsupasius” is a portmanteau honoring the institutions and societies involved in the discovery: University of Santo Tomas (UST), Romblon State University (RSU), Mindanao State University–Iligan Institute of Technology (MSU-IIT), University of the Philippines Diliman (UPD), and the Philippine Arachnological Society (PASI).

Morphologically, S. ustromsupasius is a medium-to-large, dark brown to nearly black obligate burrower that can be distinguished from S. philippinus by proportions of the legs (notably a longer first leg than fourth), details of the posterior sigilla, and characters of the male palpal organ. As of 2025, it is recognized as an accepted species in the World Spider Catalog and represents an important addition to the newly redefined, Philippines-endemic genus Selenobrachys.

Natural habitat

Selenobrachys ustromsupasius is found only on Romblon Island in the central Philippines, where it lives as an obligate burrower in disturbed, human-influenced areas. In the wild it occupies ready-made cavities under piles of coconut husks, in roadside embankments, and in the crevices of metamorphosed limestone (marble) outcrops, and has also been recorded from nearby beach forest.

Selenobrachys sp. “Romblon Pink”

Common name: Romblon Pink Earth Tiger (also sold as Selenobrachys sp. “Romblon Pink” / “Romblon Pink Tarantula”).

Origin: Endemic to the Romblon island group in the central Philippines, with hobby stocks reported from nearby Tablas Island and closely associated with the Romblon Island population recently described as Selenobrachys ustromsupasius.

Lifestyle: A fossorial Old World “earth tiger”: an obligate burrower that constructs silk-lined tunnels and chambers in loose soil, often under stones, roots or other ground cover. As with its congeners, it’s fast, secretive, and does most of its activity from the safety of the burrow entrance.

Adult size: Medium-sized tarantula. Adult females are typically in the 3.5–4 in (9–10 cm) diagonal leg span range, comparable to Selenobrachys philippinus and other Philippine Selenobrachys species.

Growth rate: Medium to fast growth rate: slings put on size reasonably quickly under warm, well-fed conditions, but don’t reach adulthood quite as explosively as some African baboon species. This estimate is based on keeper reports and the growth profile of S. philippinus.

Temperament:

• Very quick and prone to sudden bursts of speed

• More likely to bolt to its burrow than stand its ground, but will defend if cornered

• Potent venom is assumed, so this species is not recommended for handling and best suited to keepers comfortable working with defensive, fast tarantulas.

Color & appearance:

• Overall body a dusky brown to deep mahogany, with a darker carapace and abdomen.

• Legs and femurs often show a subtle pink to purplish sheen, especially in good lighting, which gives rise to the “Romblon Pink” name.

• Slings and juveniles tend to be more muted; adults develop richer tones and heavier leg setation.

• Typical Selenobrachys look: slim, “earth tiger” build, heavy leg spination, and dense webbing around the burrow entrance.

Species History

“Romblon Pink” is a hobby name for an undescribed Philippine tarantula in the subfamily Selenocosmiinae, currently treated informally as Selenobrachys sp. “Romblon Pink”. Field collectors and local enthusiasts recognized it years before any formal description, noting its distinctive pink-to-orange legs and darker body.

The spider has passed through several tentative labels in the trade (including Orphnaecus sp. and generic “Selenocosmiinae sp. ‘Romblon Pink’”) as taxonomists debated the limits of these closely related genera. n 2025, a major ZooKeys study re-examined these Asian “earth tigers,” formally revalidating the genus Selenobrachys and recognizing just two described species: S. philippinus and S. ustromsupasius, both endemic to the Philippines.

The same 2025 work described Selenobrachys ustromsupasius, the “Romblon black” tarantula from Romblon Island. Hobby discussions and at least one retailer have suggested that the pink form corresponds to this new species, but other arachnologists note that the bright “Romblon Pink” commonly kept in collections originates from nearby Tablas Island and was not directly treated in the description. As a result, most careful keepers still list their animals as Selenobrachys (or “Selenocosmiinae”) sp. “Romblon Pink” until its population is formally described.

Natural Habitat

Selenobrachys sp. “Romblon Pink” is believed to occur in the Romblon island group of the central Philippines, particularly around Tablas and Romblon Islands. This region has a classic tropical rainforest (Af) climate – warm all year (average ~25–27 °C / 77–81 °F), very high humidity (~80%+), and heavy rainfall of over 2,200 mm annually.

Like its close relative Selenobrachys ustromsupasius from Romblon Island, it is associated with lowland coastal and agricultural habitats rather than pristine mountain forest. Specimens of S. ustromsupasius have been documented using existing cavities under piles of coconut husks, crevices in metamorphosed limestone (marble) along roadside embankments, and leaf-littered beach forest near the shoreline. These areas are typically a mosaic of coconut plantations, rice fields, scrub, and remaining forest patches.

On the microhabitat level, Selenobrachys species are obligate burrowers of the forest floor. They shelter in deep, silk-lined burrows or natural cracks in the soil and rock, often just inside the entrance during the night, waiting to ambush passing invertebrate prey. The consistently warm, humid conditions and loose, organically rich ground layer of Romblon’s lowlands provide ideal conditions for these fossorial “earth tigers.”

Our Specimen:

Given name: TBD

Sex: TBD

Life stage: sling

• New addition to our collection