South American Bushmaster

Lachesis muta, also known as the Southern American bushmaster or Atlantic bushmaster, is a pit viper species found in South America, as well as the island of Trinidad in the Caribbean. Two subspecies are currently recognized, including the nominate subspecies described here.

Taxonomy

Two additional subspecies, L. m. melanocephala and L. m. stenophrys, had earlier been recognized. However, both were elevated to species level by Zamudio and Green in 1997 (see L. melanocephala and L. stenophrys).

Subspecies

Description

Adults grow to an average of 2 to 2.5 m (6½-8 feet), although 3 m (10 feet) is not too unusual. The largest recorded specimen was 3.65 m (12 feet) long, making the species the longest of all vipers and the longest venomous snake in the Western Hemisphere. Lachesis muta is the third longest venomous snake in the world, exceeded in length only by the king cobra and the black mamba. Weight in this species is estimated at an average of 3 to 5 kg (6.6 to 11.0 lb), somewhat less than the heaviest rattlesnakes (like the eastern diamondback rattlesnake) or Bitis vipers (such as the Gaboon viper and rhinoceros viper).

The head is broad and distinct from the narrow neck. The snout is broadly rounded. There is no canthus. A pair of small internasals is present, separated by small scales. The supraoculars are narrow. Other parts of the crown are covered with very small scales. Laterally, the second supralabial forms the anterior border of the loreal pit, while the third is very large. The eye is separated from the supralabials by 4-5 rows of small scales.

The body is cylindrical, tapered and moderately stout. Midbody there are 31-37 nonoblique rows of dorsal scales which are heavily keeled with bulbous tubercles and feebly imbricate. There are 200-230 ventral scales. The tail is short with 32-50 mainly paired subcaudals, followed by 13-17 rows of small spines and a terminal spine. Like most New World pit vipers, Lachesis muta exhibits defensive tail vibration behavior in response to potential predatory threats

The color pattern consists of a yellowish, reddish or grey-brown ground color, overlaid with a series of dark brown or black dorsal blotches that form lateral inverted triangles of the same color. The lateral pattern may be precisely or indistinctly defined, normally pale at the center.

Venom

Some reports suggest that this species produces a large amount of venom that is weak compared to some other vipers. Others, however, suggest that such conclusions are not accurate. These animals are badly affected by stress and rarely live long in captivity. This makes it difficult to obtain venom in useful quantities and good condition for study purposes. For example, Bolaños (1972) observed that venom yield from his specimens fell from 233 mg to 64 mg while they remained in his care. As the stress of being milked regularly has this effect on venom yield, it is reasoned that it may also affect venom toxicity. This may explain the disparity described by Hardy and Haad (1998) between the low laboratory toxicity of the venom and the high mortality rate of bite victims.