Gonyosoma jansenii
Silhouette: Alex Slavenko · PhyloPic
In 3 days ~60% in a week ~90%
Gonyosoma jansenii, commonly known as the Celebes black-tailed rat snake, the Celebes ratsnake, and Jansen's rat snake, is a species of snake in the subfamily Colubrinae of the family Colubridae. The species is endemic to the Indonesian island of Sulawesi.
The specific name, jansenii, is in honor of Albert Jacques Frédéric Jansen, who was an administrator in the Dutch East Indies. The preferred natural habitat of G. jansenii, is forest, at altitudes from sea level to 1,000 m (3,300 ft).
A long snake, G. jansenii may attain a total length of 199 cm (6.53 ft), which includes a tail length of 45 cm (1.48 ft). Adults are olive or yellowish brown on the anterior and middle portions of the body, with some scales black-edged. They are entirely black on the posterior portion of the body and tail (Boulenger, 1894).
G. jansenii is semi-arboreal. G. jansenii is oviparous. Bleeker P (1858). "Gonyosoma Jansenii Blkr, eene nieuwe slang van Manado". Natuurkundig Tijdschrift voor Nederlandsch Indië 16: 242. (Gonyosoma jansenii, new species, p. 242). (in Dutch).
Boulenger GA (1894... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Tangkoko Nature Reserve | 🇮🇩 Indonesia |
More parks will be added in future updates.
Possible
About 30% of wildlife watchers report a Celebes Black-Tailed Ratsnake sighting in Tangkoko Nature Reserve on a given day, based on 10 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 9th most-seen of the 12 reptiles we can rate there. Over three days the chance rises to about 60%, and over a week to about 90%, if each day is a fresh chance.
October
In that month about 60% of wildlife watchers report a Celebes Black-Tailed Ratsnake in Tangkoko Nature Reserve on a given day, against under 5% in January–February, April and September, the lowest months.
Between 9 am and noon
Across all the parks we cover, that three-hour window holds the most Celebes Black-Tailed Ratsnake sightings with a recorded time, and about 8 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
Only Tangkoko Nature Reserve, in our data
Tangkoko Nature Reserve is the only park on Wallace's Line with enough records to rate Celebes Black-Tailed Ratsnake sightings: about 30% of wildlife watchers there report one on a given day.
Same family: Colubridae
The closest relatives of the Celebes Black-Tailed Ratsnake that you can see in Tangkoko Nature Reserve (family Colubridae, Colubrid Snakes) are Brown Tree Snake (about 30%), Terrific Bronzeback (about 30%) and Oriental Whipsnake (about 20%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Celebes Black-Tailed Ratsnake is recorded against all the reptiles logged in Tangkoko Nature Reserve (10 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
