1837a Homalopsis
leucobalia Schlegel, Essai sur la Physionomie des Serpens. 2:345. Type locality: Timor. Holotype: RNHL
1161. Collector: unknown.
1842 Fordonia
leucobalia - Gray, Zoology Miscellany,
p. 67.
1849 Fordonia
unicolor Gray, Catalogue of Specimens
of Snakes in the Collection of the British Museum, p. 77. Type locality:
Borneo. Syntypes: BMNH 111.22.2.a. Collector: Sir Belcher. BMNH 111.22.2.b
Lowe’s collection.
1854 Hemiodontus
leucobalia - Duméril, Bibron and Duméril, Érpétologie générale… reptiles, 7:884.
1863 Hemiodontus
chalybaeus Jan, Elanco systematico
degli ofidi, p. 79. Type locality: Singapore. Holotype: possibly the Milan
Museum. Collector: unknown.
1868 Fordonia
bicolor Theobald, Journal of the Linnaean
Society of Zoology 10:56. Type locality: near Rangoon (= Yangon, southern
Myanmar.). Holotype: apparently lost. Collector: unknown.
1877 Fordonia
papuensis Macleay, Proceedings of
the Linnaean Society of New South Wales,
2:35. Type locality: Kataw, New Guinea. Holotype: Australian Museum. Collector:
unknown.
1878 Fordonia
variabilis Macleay, Proceedings of
the Linnaean Society of New South Wales,
2:219. Type locality: Port Darwin, Australia. Syntypes: three specimens,
Macleay Museum, Syndey? Collector: Mr. Spalding.
Etymology
The name leucobalia, is from the Greek leuco
meaning white, and balios meaning
spotted, dappled or piebald. This description fits several of the color morphs
from northern Australia that may be black and white spotted, or a morph with
red, black, and white spots; and it seems likely that the color morph is also
present at the type locality, Timor, Indonesia.
Distribution
At the western edge of its range Fordonia
is known from India’s Nicobar Islands, and on the coastal mainland from
Bangladesh and Myanmar it ranges eastward along the coasts of islands and the
mainland throughout Southeast Asia to the Philippines, and southward to New
Guinea and Northern Australia. It should be emphasized that like other coastal
marine homalopsids this snake probably does not occur inland or in open ocean
environments accept as waifs.
Diagnosis
In Southeast Asia Fordonia is almost always a uniform
black with a white belly, however in Australia, New Guinea and possibly in
extreme eastern Indonesia (Timor) it has multiple color morphs. Fordonia
has 23 - 27 scale rows at midbody but the most frequently encountered count is
25 rows (85%); it also has 5 - 7 (usually six) upper labials, a low count for a
homalopsid; and it usually lacks a loreal scale. Additionally, Fordonia has an internasal scale that completely separates the two
nasal scales, a character state that will immediately separate if from all Enhydris.
In its mangrove and mud flat habitat it is most likely to be confused with Gerarda
prevostiana which also has a uniform black dorsum over most of its range.
However, Gerarda has 17 scale rows at midbody. Fordonia has also been mistaken for Enhydris punctata that
has a similar number of scale rows at midbody, but it possesses a loreal scale,
has 12 or more upper labials, and nasal scales that contact each other.
Size
The largest male measured for this
study had an 817 mm total length with a 103 mm tail. The largest female had a
total length of 764 mm with an 89 mm tail. The smallest was an unsexed juvenile
that had a total length of 192 mm with a 19 mm tail. Rooij (1917) mentioned a
specimen that had a total length of 930 mm and a 110 mm tail. Smith (1943)
reported a male that had a total length of 780 mm with a 100 mm tail and a
female that was 1065 mm in total length with a 125 mm tail. Bergman (1960)
suggested newborns are less than 180 mm SVL, and adults are sexually mature at
330 mm SVL. His largest male had a total length of 606 mm, and a 95 mm tail;
his largest female had a total length of 637 mm with a 72 mm tail. Bergman
(1960) noted males have longer tails than females, and reported that Kopstein
found females to have 32 - 36 subcaudal scales; males have 39 - 45 subcaudal scales
in the Java population. The tail/SVL ratio for the New Guinea population determined
during this study was 14 - 18% in males and 12 - 15% in females (males n = 10,
females n = 8).
At
the base of the tail the width is 75% of the height, based on the average of
five specimens. Karns et al. (2002) studied this snake at Pasir Ris Park in
Singapore and took measurements on 19 snakes; their data is summarized in Table
16.
External
Morphology
The head is slightly
distinct from the neck; it is short and very depressed. The eye diameter is
slightly less that the eye-nostril distance. The lower jaw is countersunk. The
tail is compressed.
On the head the
rostral scale is rounded and barely visible from above. All of the head plates
are imbricate. The nasals are semidivided (rarely entire), the nasal cleft may
touch the prefrontal or the internasal, and in rare instances where a loreal is
present the nasal cleft may touch that scale. The nasals are separated by the
internasal. The internasal is single and slightly smaller in area than a single
nasal. The prefrontals are about the same size as the nasal and they touch the
loreal, the nasal, and the supraocular. The frontal is about 80% of the
interorbital distance. The parietals are about 1.2 times the length of the
frontal. The supraocular is elongated with rounded anterior and posterior
margins, the preocular is single, there are two postoculars, and the bottom
scale is larger than the upper scale. Loreal scales are usually absent. There
are two primary temporal scales, the upper one is very large. Upper labials
number five (rarely six), the largest is usually four or five, and the third
(rarely the second) enters the orbit. On the chin the lower
labials number 5 - 7 (usually six), and the first three contact the anterior
chin shields. There are two pairs of chin shields (rarely one or three); the
anterior pair is usually the largest; the second pair if present are in contact
with each other. Gular scales number 3 - 6. On the body the dorsal
scale rows number 25 - 27 on the neck; at mid-body dorsal scale rows number 23 -
27 (usually 25 - 85% of the time). Posterior dorsal scale rows are reduced to
21 - 23. The ranges of dorsal scales are somewhat misleading in that most
specimens have 25 scale rows at mid-body, three (11.5%) specimens of 26 had 23
rows, and one (3.8%) specimen of 26 had 27 rows. The dorsal scales are
imbricate, smooth, lanceolate (even the first row tends to be elongate), and
scales have fine striations, otherwise they are smooth. Near the vent the
scales become ovate and this shape continues onto the tail. The ventral scales
number 140 - 150. They are wide, about three times the height of a nearby
dorsal scale. No indication of sexual dimorphism or geographic variation in ventral
scale counts was detected; males have 142 - 150 ventral scales, females have 140
- 150. The anal plate is divided; it is about twice the length of the preceding
ventral scale, and the Singapore population has the ventral preceding the anal
plate divided. Additionally, Karns et al (2002) reported sexual dimorphism in
the anal plate. On the tail the
subcaudal scales are usually divided, however some individuals have mixed
subcaudal scales (some single and some divided scales), they number 28 - 41. In
the Malaysian-Singapore population males have 29 - 34 subcaudal scales and
females have 28 - 29. However, the New Guinea population has males with 35 - 41
subcaudal scales and females with 30 - 34. Gyi (1970) observed that, “Males
have a slightly longer and more compressed tails than females. In males the
tail is provided with a dorsal hump extending from the level of the fourth to
about the 26th subcaudal. In females the tail gradually tapers to a
point.”
Color and Pattern Most of the specimens
examined from Southeast Asia have a uniform black dorsum and a white belly.
However, the Australia-New Guinea population shows dramatic color and pattern polymorphism.
Gow (1989) reported six color morphs and O’Shea (1986) noted five different color
morphs in the Western Province, Paupa New Guinea, and notes that no two
specimens had the same color pattern. Color morphs I have seen include: (1) a
uniform gray-black dorsum with the first two or three scale rows cream; (2) a
black dorsum with white cross bars or spots on the vertebral line and lateral
white spots or mottling; (3) a red dorsum with white crossbars each bordered in
black; (4) a yellow or orange dorsum with black vertebral spots or crossbars.
 |
| Singapore. |
Habitat
This is a snake of the mangrove forest and associated mud flats. It may
on occasion enter surrounding habits such as monsoon forest or open ocean
(O’Shea, 1986; Campden-Main, 1970) but it is unlikely that these areas are
supporting populations of this species.
Fordonia
uses the intertidal burrow system. Karns et al. (2002) monitored the movements
of three male snakes over a period of five weeks using radiotelemetry in
Singapore’s Pasir Ris Park, a mangrove forest. Snakes monitored for 7 - 10 days
were relatively sedentary (46.6% of the days they were inactive) and when they
did move it was only for short distances (1.8 - 14.0 m, = 4.4 m).
Two of the snakes were always located in mud lobster mounds (100% of the
telemetric locations), but did not show a preference for lobster mounds of a
particular size. A third snake used the mud-root tangle of the mangrove 59% of
the time, and an area under a boardwalk the other 41% of the time. It was
usually associated with two mud lobster mounds. While these individual snakes
frequented the mud lobster mounds and the landward edge of the mangrove, they
were observed foraging on tidal mud flats. Body temperatures (26.3 - 29.0°C, = 28°C)
for these three snakes were consistently above the temperature of the
microhabitat they were using and significantly different. Of the three
monitored snakes only one moved once during the day, and all other activity was
nocturnal, and the snakes were active throughout the night.
 |
| Nt, Australia |
The literature supports
the idea that this species uses mangrove forests, mud flats, and makes use of
crustacean burrows across its distribution. Macnae (1968) described this species in the
mangrove habitats of the Malayan Peninsula and Thailand. In Java, Kopstein
(1931) stated that they live in crab burrows; and Hoesel (1959) described them
hiding in holes in the mud. In Australia, Cogger (1981) reported mangrove
habitat. And, Gow (1989) wrote, “A nocturnal aquatic species which inhabits
mangrove flats along estuaries, creeks and rivers. At low tide it shelters
among mangrove roots or down crab holes.” Worrell (1963) stated it occurs, “…in
mangrove roots in colonies. I have seen them crawling along mudbanks at low
tide…not often found in fresh water unless tidal.” In New Guinea, Parker (1982) found them 250 m
from the high tide mark; and O’Shea (1986) found them on a path, along a river;
on mud flats; and in crab burrows, including, a crab burrow on a village
street. Like other homalopsid species that use mudflats this species can use
sidewinding locomotion (Cogger and Lindner, 1974).
Diet and Feeding
Behavior
Ever since Günther (1864) recognized
that it feeds on crustaceans, most authors writing about this snake have discussed
its unusual carcinophagus diet. And, several authors report their own
observations. In Australia, Gow (1989) wrote, “It feeds upon small crustaceans
and when hunting forages amongst dense mangrove roots, broken pools and
channels. The author has recorded it feeding on fiddler crabs (genus Uca) and a mud lobster Thalassina anomala.” And, Shine (1991a)
dissected 75 specimens and found 60 crabs, many were Uca, he also found one that contained a mud lobster, and two
unidentified shrimp. In New Guinea, Parker (1982) reported small red and black
mud crabs as food. McDowell (in Parker) reported nematodes in almost every
stomach, and consistently found crabs, with the exception of one orthopteran
insect in one specimen. Voris and Murphy (2002) reported the following crab
taxa from Fordonia: Sarmiatium germaini, Macrophthalmus sp., and a sesarmine crab
(Grapsidae) as well as Dotillopsis
brevitarsis and Uca sp.
(Octpodidae). Crab remains from five stomachs suggest these snakes use
relatively small prey, 0.5 - 7.4% of the predator’s mass (Voris and Murphy,
2002). One specimen (MAGNT R.5270) a 44 cm SVL male was found carrying a 29.2 g
mud lobster (Thalassina anamala) (carapace length 44.9 mm, total length
132 mm) in its mouth. Nobbs and Blamires (2004) describe diurnal feeding, and
observed F. leucobalia coiling around
a crab (Uca flammula), apparently in
an attempt to secure it. They also observed two instances of F. leucobalia swallowing a mud lobster
tail and separating the tail from the cephalothorax and report hearing audible
crunching. In one of these instances one snake attempted to steal a mud lobster
from another snake. Separation of mud lobster tails clearly does not occur all
the time since this author has removed whole Thalassina from snake digestive systems.
Glauert (1950) and Worrell (1963)
mention frogs in its diet, this seems highly improbable, although in Southeast
Asia the crab-eating frog Rana
[=Fejervarya] cancrivora inhabits mangroves and uses mud
lobster mounds, thus the opportunity is present, and it is not inconceivable
that a frog eating a crab or a crab eating a frog could be encountered by a
snake and ingested accidentally. Similarly, Hoesel (1959), Worrell (1963) and
Campden-Main (1970) included fish in this snake’s diet, prey that seems highly
improbable, but accidental ingestion is always a possibility.
Several aspects of prey handling in Fordonia have gained attention because
they seem to deviate from typical snake behavior. Hoesel (1959) wrote, “It is
exciting to observe a Fordonia catching
a crab. In a flash the crab is constricted and the snake waits in this position
till the victim has quieted down by the influence of its poison.” Shine and
Schwaner (1985) described Fordonia
pressing crabs into the mud and holding crabs in a coil while removing the
animal’s legs. And, O’Shea (1996) wrote, “Crabs are pinned in their burrows and
‘chewed’ until they are dismembered.” Shine (1985) and Voris and Murphy (2002)
report them pinning crabs into the mud with their chin, and using the crab’s
own defense behavior to immobilize the crustacean; swallowing small crabs with
the strike, and Voris and Murphy (2002) suggested that the crabs may autonomize
their own legs rather than having the snake “chew” them off.
Savitzky (1983) proposed that Fordonia crushes its prey using “hypertrophied
cranial kinesis.” Crushed crabs in snake stomachs, which would support this
view, have not been found by me. However, the fangs of this species are
particularly robust and the heavy musculature of the skull may be used to apply
enough pressure to the crab’s exoskeleton via the fangs so that the fang can
puncture the exoskeleton and deliver venom and/or digestive enzymes to the
crab’s tissues. These robust fangs and associated musculature may also be used
to remove the mud lobster tail from the rest of the body as reported by Nobbs
and Blamires (2004).
Reproduction
Litter size. The range
reported by Shine (1991a) of 2 - 17 (n = 15, = 6.1) spans the ranges of all others reported in
the other literature. Kopstein (1932; 1938) reported Indonesian females with 3 -
5 embryos (= 4); Gyi reported a specimen with 13 eggs; Parker
(1982) reported the range of 2 - 11. Gravid female SVL’s reported by Parker
(1982) ranged from 521 - 720 mm.
Timing of reproduction
was reported by McDowell (in Parker, 1982) based upon a series of snakes
collected at Agats (Irian Jaya, Indonesia) in March, as well as specimens from
the Western Province. Parker wrote,
He [McDowell] has reconstructed the reproductive
calendar for the south coast as: eggs becoming mature June-July, when breeding
takes place. Perhaps August to September through to December and January,
embryonic development taking place. February and March fetuses identifiable and
birth of young. April to June, eggs developing.
He found that a Queensland specimen agreed well with
this timetable, but that Broome (Western Australia) specimens differed
considerably, and that the Broome population had many morphological differences
from the populations of southern New Guinea and Queensland.
One museum specimen
examined (MAGNET R.6201), a female (425 mm SVL) gave birth to eight young on 24
November. This is the smallest gravid female reported to date.
Size of neonates was
reported by Parker (1982) from specimens collected from January to March. They
ranged in total length from 176 - 196mm (= 188.5), and had tails that were 22 - 24mm (= 23.5). Gow (1989) reported neonate size as 180
mm in length
Predators and
Parasites
Lyle and Timms (1986) reported five snakes taken from the stomachs of
four specimens of the nervous shark, Carcharhinus
cautus, in Darwin Harbor, Northern Territory. An unnumbered MAGNT specimen
of Varanus indicus, from Adelaide
River Creek, NT contained a Fordonia
leucobalia that was about 350 mm in total length. The lizard has an SVL
length of about 40 cm. The lizard specimen is unregistered and on display at
MAGNT. Guinea (in Greer, 1997) reported that the bird commonly called the
jabiru (Xenorhynchus asiaticus) feeds
on this snake. Loveridge (1948) reported the nematode Ortleppina longissima from the stomach of one specimen.
Populations, Abundance,
and Activity
Parker (1982) wrote
about the abundance of this species, “At times many hundreds of these snakes
have been found in the mangroves of Daru and Bobo Islands [New Guinea]. At
other times only odd individuals can be found. In some cases, these large
numbers appeared to coincide with extra high tides. At those times, many of the
snakes were gravid females with large eggs lacking embryonic development.”
Karns et al. (2002) found no association between tides and the activity of this
species at Pasar Ris, Singapore; but at this study site the tidal cycle had
been modified by human alteration of the drainage system. However, they did get
the impression that snake activity was higher on days with late afternoon or
early evening showers.