Achalinus formosanus
{{Short description|Species of snake}}
{{speciesbox
| image = Achalinus formosanus formosanus full body shot.jpg
| image_caption = Achalinus formosanus formosanus
| status = LC
| status_system = IUCN3.1
| taxon = Achalinus formosanus
| authority = Boulenger, 1908{{cite journal |last1=Boulenger |first1=G. A. |year=1908 |title=Description of a new frog and a new snake from Formosa |journal=Annals and Magazine of Natural History |volume=8 |issue=2 |pages=221–222 |doi=10.1080/00222930808692472 |url=https://www.biodiversitylibrary.org/bibliography/15774}}
| range_map = Achalinus formosanus distribution.png
| synonyms = Achalinopsis sauteri Steindachner, 1913
}}
Achalinus formosanus, common name Formosan odd-scaled snake or Taiwan burrowing snake, is a non-venomous snake in family XenodermidaeIn earlier classifications sometimes still in use, subfamily Xenodermatinae, family Colubridae. See e.g. {{ITIS|id=700178 |taxon=Xenodontinae Cope, 1895 |accessdate=1 November 2015}} that is found in Taiwan and in the southern Ryukyu Islands (Japan).{{NRDB species|genus=Achalinus |species=formosanus |accessdate=1 November 2015}}{{cite web|author=Hans Breuer|author2=William Christopher Murphy|name-list-style=amp|date=2009–2010|url=http://www.snakesoftaiwan.com/Achalinus%20formosanus/species_achalinus_formosanus.htm|title=Achalinus formosanus formosanus|work=Snakes of Taiwan|access-date=1 November 2015|archive-date=25 February 2020|archive-url=https://web.archive.org/web/20200225193446/http://www.snakesoftaiwan.com/Achalinus%20formosanus/species_achalinus_formosanus.htm|url-status=dead}}
Taxonomy
There are two subspecies:
- Achalinus formosanus formosanus Boulenger, 1908 — Taiwan
- Achalinus formosanus chigirai Ota and Toyama, 1989 — Ryukyu Islands{{cite journal |last1=Ota |first1=Hidetoshi |last2=Toyama |first2=Masanao |year=1989 |title=Taxonomic re-definition of Achalinus formosanus Boulenger (Xenoderminae: Colubridae: Ophidia), with description of a new subspecies |journal=Copeia |volume=1989 |issue=3 |pages=597–602 |jstor=1445485 |doi=10.2307/1445485}}
Specific name formosanus means "from Formosa", referring to the fact that this species was first described from a specimen from Taiwan. chigirai refers to Yoshinori Chigira, who collected the first specimen of Achalinus formosanus chigirai.
Achalinus formosanus formosanus is ecologically and morphologically similar to the Taiwan endemic Achalinus niger; the two differ in some scale counts and characteristics. A study using genetic markers found these two taxa to be overlapping, warranting further studies on their taxonomy.{{cite book |title=Phylogeography of Odd-scaled Snake Achalinus in Taiwan |last=Shie |first=Jia-Rung |year=2006 |publisher=Masters thesis, National Sun Yat-sen University |pages=53 |url=http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/getfile?URN=etd-0725106-173423&filename=etd-0725106-173423.pdf}}
Distribution
Achalinus formosanus formosanus is known from central and southern Taiwan at elevations of {{convert|1000|–|2000|m|abbr=on}} asl. Achalinus formosanus chigirai occurs at low altitudes (below {{convert|200|m|abbr=on}}) on the Iriomote-jima and Ishigaki Islands, both belonging to the Yaeyama Group.{{cite journal |last1=Ota |first1=Hidetoshi |last2=Toyama |first2=Masanao |year=1989 |title=Two additional specimens of Achalinus formosanus chigirai (Colubridae: Ophidia) from the Yaeyama Group, Ryukyu Archipelago |journal=Japanese Journal of Herpetology |volume=13 |issue=2 |pages=40–43 |doi=10.5358/hsj1972.13.2_40 |url=https://www.jstage.jst.go.jp/article/hsj1972/13/2/13_2_40/_article|url-access=subscription }}
Description
File:Achalinus formosanus formosanus close-up with tongue extended.jpg
Achalinus formosanus is a small snake growing to a total length of about {{convert|90|cm|abbr=on}}. The whole body is iridescent under light. Head is small, oval, and without distinct neck. Body is slender and tail is moderately short. Eyes are small, bead-like; iris is black and indistinct. Upper head, body and tail is uniform olive, grayish tan, or black. Mid-dorsal row of scales on body and tail show a dark longitudinal line. Ventral surface is olive-yellow or dark gray. The young are usually black.
Behaviour
Achalinus formosanus has been reported to eat earthworms.{{cite journal |last1=Fukuyama |first1=Ryobu |last2=Fukuyama |first2=Ibuki |title=Achalinus formosanus chigirai (Yaeyama Odd-scaled Snake). Defensive Behavior and Diet. |journal=Herpetological Review |date=1 March 2021 |volume=52 |issue=1 |pages=144-145 |url=https://www.researchgate.net/publication/349988276_Achalinus_formosanus_chigirai_Yaeyama_Odd-scaled_Snake_Defensive_Behavior_and_Diet |access-date=17 April 2025}} It may also prey on slugs and frogs. It is a nocturnal, terrestrial snake that is non-venomous and not aggressive. It is oviparous.
Habitat and conservation
Achalinus formosanus formosanus are found in montane humid forests, where they live in dark, wet micro-habitats such as the forest floor, rotten wood, and leaf litter. Achalinus formosanus chigirai have been collected in on a road at night and in a limestone cave in the daytime as well as in low grass along a path in the evening and on forest floor at night.
No significant threats are known. It is not a protected species in Taiwan, but Achalinus formosanus chigirai is classified as "near threatened" in Japan.