Black Jansens Rat Snake

Common Name: Black Jansen’s Rat Snake
Scientific Name: Gonyosoma jansenii
Source: WC

Adult Size: Around 120 cm typical; larger individuals reported
Native Range: Sulawesi and nearby islands, Indonesia

Enclosure: Tall, secure arboreal vivarium with lots of climbing branches and cork tubes; from ~90 × 45 × 90 cm for an adult
Heating (Basking / Ambient / Night drop): Day 26-29 °C with a local warm spot around 32 °C; night 22-24 °C

Humidity (range + ventilation note in one line): 60-90% with strong ventilation; daily misting with time to dry off between sprays

UVB: Not reliably verified; bright day lighting recommended, with shaded retreats

Diet: Primarily rodents; birds/lizards are reported in the wild

Water: Large, clean water bowl provided at all times; many individuals drink readily after misting

ABOUT THIS SPECIES

Jansen’s rat snake is a slim, semi-arboreal Indonesian colubrid known for its alert “canopy hunter” look laterally compressed body, long tail, and a strong preference for elevated perches. The black form is especially striking, typically showing an inky, glossy finish that reads jet black under bright light. In the wild the species is associated with forested habitat on Sulawesi and nearby islands, and it spends much of its time off the ground, moving through branches and dense cover.

A well-built vertical enclosure makes a big difference: plenty of climbing routes, multiple snug hide options at different heights, and a clear warm-to-cool gradient so it can choose its preferred perch temperature.