Ferania sieboldi (non Schlegel) Günther, 1866 Annals and Magazine of
Natural History, ser. 3, 18:28.
Hypsirhina gigantea Werner, 1923a Annalen des Naturhistorischen Museum
in Wein, 36:163. Type locality: unknown. Collector: unknown. Holotype: Vienna
Museum.
Enhydris bocourti - Smith, 1930 Bulletin of the Raffles Museum 3:61.
Hypsirhina bocourti soctrangensis Bourret, 1936 Serpentes de
I'Indochine, 1:291. Type locality: Soc Trang, Vietnam. Holotype: MNHN 38144. Collector:
unknown.
Subsessor bocourti Murphy and Voris 2014: 34.
Eytmology: This snake was named to honor the 18th-century French
herpetologist Marie-Firmin Bocourt. Common Names: Bocourt's Water Snake (Smith,
1943); Ri voi snake (Thu, 2001) Vietnam
Distribution: This snake is endemic to the Indochinese peninsula,
including Thailand, Malaysia, Cambodia, and Vietnam. Deuve (1970) reported it
from the river side towns of Ngou Pa and Ngou Leuam in Vientiane Province, Laos. It is unclear if
this is the northern edge of the distribution, an isolated population, or possibly
a feral population. I have not yet examined specimens from this area. Theobald
(1868) has reported it from India and Burma (Myanmar). Hundley (1964) also
reports it from Burma possibly based upon Theobald’s record. These localities
are most likely in error based upon confusion with specimens of Enhydris
sieboldi. The confusion may extend to erroneous statements made by Günther
(1866; 1868) that the illustration labeled sieboldii in Jan and Sordeli (1860 -
1881) was actually bocourti. Specimens documenting its presence west of central
Thailand have not been found, but it does occur on the southern edge of
Thailand’s Khorat Basin and is likely to be more widespread in the Mekong
drainage than current data suggests. It may eventually be shown to be present
in southern Myanmar since it is known from southern Thailand. Its distribution
forms an arc around the Gulf of Thailand, a distribution similar to that shown
by the snakes of the Enhydris jagorii Group and Erpeton tentaculatus. Recent
reports of this species from China (Li, 1998) are most likely based upon its
presence in markets or feral animals; S. bocourti is imported into China from
Cambodia and Vietnam and if Chinese populations are found they are most likely
the result of escaped market animals or intentional release.
Diagnosis: A large, robust homalopsid with 27 scale rows at mid-body;
divided upper labials behind the eye; 135 ventral scales, or fewer; and an
internasal that is single, and may make narrow contact with the loreal scales.
Size: The largest specimen measured was a female from Thale Noi, in
southern Thailand, with a total length of 1,230 mm, and a 150 mm tail; this
individual was gravid and weighed 2.8 kg. The largest male measured had a total
length of 770 mm, with a 124 mm tail. The smallest individual measured was 154
mm in total length with a 27 mm tail; this is probably near the low end size at
birth, and this species as well as Homalopsis
buccata probably give birth to the largest homalopsid neonates. Gyi (1970)
was confused when he said this was the longest homalopsid, and cited USNM 70302
as the largest specimen at 1,375 mm. USNM 70302 is a Homalopsis buccata, collected by H. Smith and discussed and
illustrated by Cochran (1927; 1930). While bocourti
is not currently known to be the longest homalopsid, it may the one with the
greatest bulk. Smith (1914) reported a 1,120 mm individual. Saint Girons’
(1972) largest specimen was a 950 mm female; his largest male was 812 mm total
length, he also described a sexually mature female that was 590 mm. Werner
(1923a) described one that had a total length of 1075 mm and a 125 mm tail;
this is the type specimen of Hypsirhina
gigantea.
External Morphology: The head is short and slightly distinguishable
from the neck. The eyes are dorsolateral. The body is extremely thick in girth
and slightly compressed. On the head the rostral scale is pentagonal, is as
broad as tall, and two notches are barely discernable on the ventral edge. The
nasal is semi-divided or divided with the nasal cleft touching the first labial
or the first labial and internasal. The internasal is usually single, but
divided in one specimen, and smaller than the nasal. The internasal is behind
and slightly penetrating the nasals. The prefrontals are in contact with the
loreal scales. The frontal is elongated and pentagonal or bullet-shaped. The parietals are about as long as the
frontal and they have light or dark spots or blotches. The loreal is single and
is in contact with 1 - 2 or 1 - 3 upper labials. The single supraocular is
narrow anteriorly and widened posteriorly. On two specimens there is a fragment
of this scale on the posterior ventral edge. The preocular is usually single,
but subdivided in one specimen, and there are two postoculars and no subocular
scales. Temporal formula is 1 + 2 + 4. Upper labials number eight (rarely
nine), the fourth is in contact with the orbit and some of the upper labials
posterior to the eye are horizontally divided. The largest upper labial is six
or seven, and there are very small tubercles on the labials. On the chin, lower
labials number 11 - 14, with the first labial being the largest. The anterior
pair of chin shields is 3 - 4 times longer than the second pair. The anterior
chin shields are in contact with the first five (or four) lower labials. The
second pair of chin shields is separated by a pair of smaller scales. Nine or
10 gular scales separate the chin shields from the most anterior ventral scale.
On the body the dorsal scales are in 27 - 29 rows on the neck, these are smooth
and ovate and become only slightly lanceolate on the midline; three specimens
from peninsular Malaysia have 29 scale rows on the neck, while Cambodian and
Vietnam specimens tend to have 26 - 28. Dorsal scale rows at mid-body number
27; they are smooth and or slightly textured, and they are mostly ovate,
becoming only slightly elongate toward the midline. The dorsal scales at
posterior body are similar and are in 21 - 25 rows. The ventral scales at the
anterior of the body are narrow, and about three times the height of a nearby
dorsal. The ventrals at mid-body are about 3.5 times the height of a nearby
dorsal, and those at posterior body are about three times the height of a
nearby dorsal. Ventral scales number 123 - 135 (129 - 133 in males, 123 - 135
in females). The anal plate is divided. On the tail dorsal scales are ovate,
smooth, but slightly textured. The subcaudal scales are divided and number 32 -
47 (41 - 47 in males, 32 - 37 in females). At the base of the tail the width is
81% of the height, based on the average of five specimens. Color and pattern.
The dorsum is dark brown with 30 - 40 transverse crossbars that are one scale
wide; one specimen (MCZ 5969) lacks the crossbars. The crown of the head is
dark brown with some dark or light spots on the head shields. There is a
post-parietal transverse bar. The upper and lower labials are yellow with some
dark seams. The venter is yellow and crossed with 25 bars of dark pigment that
are connected to the dark dorsum. Yellow blotches on the sides go to scale rows
six or seven and are 4 - 5 scale rows wide. The tail is dark brown with yellow
spots on top and below. Boulenger’s (1903) commented on the juvenile
coloration, "The superior brilliance of coloration of young specimens is
remarkable.” Sexual dimorphism. Tail/SVL ratios for males were 17 - 23%, and
for females 13.4 - 16.2%. Males have a slightly constricted area at the base of
the tail. Males have 41 - 46 subcaudal scales, while females have 35 - 40
subcaudal scales. Thus both relative tail length and the number of subcaudal
scales are sexually dimorphic in this species.
Habitat: This highly aquatic snake uses swamps, shallow lakes, pools,
and other stagnant water habitats. This snake is often found with Acrochordus javanicus in swamps and
pools; and it may move into deep water during the hottest part of the year
(Laidlaw; 1901; Boulenger, 1903).
Campden-Main (1970) stated that it is almost entirely aquatic. Deuve
(1970) reported on bocourti in Laos, it was collected in June and November from
fish traps; it fed on fish; and was mostly nocturnal. Smith (1943) found
"It is not uncommon in the low lying country in the vicinity of Bangkok
and in Cochin China." And, Taylor (1965) reported two specimens from
Pattani, Thailand that were obtained from "a pool in that city."
During this study specimens were obtained from reservoirs, rice paddies, and
shallow pools in wetland habitats in Thailand. This species also makes up a portion
of the Tonlé Sap snake harvet in Cambodia.
Subsessor bocourti inhabits
the Indochina Bioregion of Wikramanayake et
al. (2002), and extends into peninsular Malaysia (part of the Sunda Shelf
and Philippines Bioregion).
Diet and Feeding Behavior: A specimen (FMNH 259282) from Tonlé Sap,
Cambodia (male, SVL 49 cm, TL 60.5cm) contained a 10.5 cm catfish, Mystus mysticetus (Siluriformes:
Bagridae). A neonate (SVL 210 mm) obtained near Kabin Buri, Thailand contained
a 145 mm freshwater eel (Monopterus albus,
Synbranchidae). Several other specimens from the same locality contained
unidentified fish remains. Flower (1899) reported that captive newborns
"...fed readily on small frogs (Rana
and Microhyla)." Saint Girons
(1972) reported five fish in the stomach of one specimen.
Reproduction: Flower (1899) wrote,
"...While in captivity brought forth seventeen young, alive. They were
expelled at intervals of from two to twenty minutes..." He stated that the
neonates were "…about 220 mm in length." The female was 845 mm total length. Saint
Girons and Pfeffer (1972) consider this species to have a "spring
hatching" in Cambodia. Saint Girons (1972) reported 6 - 17 eggs in eleven
females from Cambodia. A female obtained at Thale Noi, Thailand, had a total
length of 1,230 mm and a 150 mm tail, and weighed 2,880 g. It contained 26
embryos, 15 in the right oviduct and one infertile egg, and 11 in the left
oviduct with three infertile eggs. The clutch weighed 667 g. There was one set of twins in the litter. The
RCM for this litter was 0.23. A second gravid female (SVL = 910 mm, total
length 1030 mm, 1.25 kg) from the Kabin Buri, Thailand area contained 28 near
full term embryos on 22 June. The mean SVL of the embryos was 17.8 cm (r = 15.4
- 19.0) and the mean mass was 9.3 g (r = 5.5 - 10.8) (Karns et al., 2005).
Predators and Associated Behavior: Campden-Main (1970) stated that the
Vietnamese sell bocourti for food
around Can Tho. Thu (2001) recognized that this species was important to local
people and economies. In Cambodia, (Stuart et
al., 2000; Brooks et al. 2007) bocourti
was part of the Tonlé Sap snake harvest although it represented a low
percentage of the harvest and it was used for human consumption and its skins
were used in the leather industry. This species was selectively removed from
the catch and sold for export to Vietnam, and presumably re-export to China.
Live specimens sold for the equivalent of US $5.21 - 6.51 per kilogram. While
dead specimens sold for US$2.61. The live snakes were more valuable because
they could be exported. Lau (in Stuart et
al., 2000) reported bocourti
common in the wildlife markets of Guangzhou, China, an area outside the
distribution of bocourti. And,
photographs in Lao (1997) suggest that the Chinese may be culturing this
species. In southern Viet Nam these
snakes are also exploited, and Stuart (2004) reported that they are the second
most abundant reptile species in trade. It sells for US $10.99/kg, and people
in the area raise them in cages until they attain a weight of about 2 kg. In Cambodia,
Brooks et al. (2007) report the
species sells for US$2.50 to 5.00 per kg.
In Laos, Deuve (1970) found them to be very irritable, and he noted
they bite readily. His samples showed
wounds which he attributed to fights, scars were numerous on the ventral
scales; these are more likely due to attacks by predators than conspecifics.
Smith (1943) commented that "Its temper is uncertain, and its large size
enables it to inflict a very serious bite if handled carelessly." My
limited experience with this species suggests that it is docile when handled
gently and shows no inclination toward biting.
Population and Abundance: Smith (1914b) considered bocourti rare in Bangkok, but common in the rural areas surrounding
it. Tweedie (1950) stated that bocourti is
poorly known from the Malayan Peninsula. At the time of writing Tweedie knew of
only three specimens, Flower’s specimens, one collected from Trengganu in 1947,
and a photo of one from Wellesley Province taken in 1947. My experience with
this snake suggests that it is relatively abundant in some areas (Kabinburi,
Thailand and Tonlé Sap, Cambodia) but nowhere did it dominate the aquatic snake
assembly like E. enhydris or E. plumbea.
Venom: The LD50 for the venom of this species was found to be 7.3 mg/kg
of body weight (Sakai et al., 1984;
Minton, 1996).