Boiga melanota, (BOULENGER, 1896)

Bringsøe, Henrik, 2020, Severe head injury in Boiga melanota (Boulenger, 1896) observed in the southeastern corner of Thailand, Pod @ rcis 11 (2), pp. 51-58 : 52-53

BOIGA MELANOTA (BOULENGER, 1896)

– WESTERN MANGROVE CAT SNAKE

Until recently the Mangrove Cat Snakes, or just Mangrove Snakes, of Thailand were considered to belong to the species Boiga dendrophila (Boie, 1827), subspecies melanota . But in a phylogenetic study based on sequencing of mitochondrial and nuclear DNA, melanota was elevated to species level ( WEINELL et al., 2020). The taxon Boiga tanahjampeana proved to be the sister taxon of melanota , which caused dendrophila s.l. to be paraphyletic. Since the authors preferred to maintain the species level status of the morphologically distinct tanahjampeana , elevating B. dendrophila melanota to the taxonomic status of a species was required.

Members of the B. dendrophila complex are not likely to be confused with any other species in their habitat: the body colour is deep black with yellow vertical bars, although cases of melanism or the yellow pattern replaced by a whitish coloration occur ( VOGEL, 2000). The head is black above with bright-yellow, blackedged labials. The chin and the anterior part of the throat are yellow. They are large colubrids attaining a total length up to 250 cm, allegedly even 280 cm, and the body is vertically compressed. They are rear-fanged and venomous with enlarged grooved maxillary teeth and the palatine teeth are also enlarged ( SMITH, 1943). Though several colubrids like the genera Dispholidus , Philodryas , Rhabdophis , Tachymenis and Thelotornis contain species responsible for serious (including fatal) human envenomations, B. dendrophila s.l. and other members of the genus Boiga are generally not considered dangerous to humans and other large mammals ( MINTON, 1990; DAVID & INEICH, 1999; SAVIOLA et al., 2014; WEINSTEIN, 2017). Earlier studies of Duvernoy’s secretions of B. melanota determined by injection in mice demonstrated low lethal potency ( WEINSTEIN & SMITH, 1993; MACKESSY, 2002). Their toxins are, nevertheless, tremendously powerful to other vertebrates.

B. melanota is a common arboreal species in South Thailand where it occurs in a variety of evergreen and mixed dipterocarp forests, including secondary forests ( CHAN-ARD et al., 2015). It is usually found in well-watered areas such as edges of streams, rivers and mangrove swamps ( GRISMER, 2011). It is also a good swimmer. In spite of their nocturnal habits members of the B. dendrophila complex are commonly encountered during the day coiled in branches though it may also retreat into tree holes ( DAVID & VOGEL, 1996; GRISMER, 2011). Being large and conspicuously coloured they may be easily detected and potentially killed by humans.

The diet of B. dendrophila s.l. is well documented and consists of a wide variety of birds and lizards, but regularly mammals, snakes and frogs are eaten, and to a small extent even crabs, slugs and possibly fish ( GREENE, 1989, VOGEL, 2000, BRINGSØE, in press).

OBSERVATIONS

At 20:25 h on 25 February 2020 (one hour after sunset), north of Hala Bala , Chanae district , Narathiwat province, Thailand (5.82477° N, 101.84714° E; WGS 84; 50 m elev.), the author observed an adult B. melanota (184 cm total length, see fig.2 ) swimming in shallow water near the bank of the Ba La River , a tributary to the larger Ko Lok River which forms the border to Malaysia. The habitat was uncultivated land with scattered trees and shrub vegetation along the stream, and bordered rubber plantations ( fig. 3 ). This individual showed a severe injury on the left and posterior part of the head's dorsal side ( figs. 4-5 ). The wound was deep and had especially affected the left labial region, and a considerable portion of the underlying bone had been destroyed and was missing. Hence the mouth could not close properly on the left side. The wound also reached the dorsal side of the head just behind the left eye. Here it was bifurcated: the larger cut went from behind the eye obliquely toward the median line of the head, whereas a minor cut started from behind the eye obliquely towards the neck. A superficial scar appeared in the left side of the anterior part of dorsum ( figs. 5-6 ).

There was no indication of infection and though the wounds were not fully healed, they seemed to be in the process of healing. The underside of the head and of the anterior part of the body proved undamaged and without any sign of injury or wound. Possibly the left venom gland had been destroyed. The snake appeared well-nourished, strong, aggressive and healthy, so the critical phase might have been passed successfully.

Figures

Figure 2. The author with the adult Boiga melanota, total length 184 cm, found in shallow water of the major stream. Photo: Sulfadlee Hagisanawee

Figure 3. The ha- bitat where Boiga melanota was found at night. It was observed in the water near the bank in front of the person. Photo taken on 6 July 2020 by Sul- fadlee Hagisana- wee

Figure 4. Adult Boiga melanota with a severe and deep injury on the left side of the head.

Figure 5. The head injury of Boiga melanota was apparently without infection and in the process of healing. Notice there was also a mild injury on the left side of the front of the body.

Figure 6. The adult Boiga melanota, total length 184 cm, found in shallow water of the major stream.