Bothrops jararaca

Bothrops jararaca — known as the jararaca or yarara is a species of pit viper endemic to southern Brazil, Paraguay, and northern Argentina. The specific name, jararaca, is derived from the Tupi words yarará and ca, which mean "large snake". Within its geographic range, it is often abundant and is an important cause of snakebite. No subspecies are currently recognized.

This is a slender and terrestrial species that grows to a maximum total length of 160 cm (63 in), although the average total length is much less.

The head scalation includes 5-12 intersupraoculars that are weakly keeled, 7-9 supralabials (usually 8) of which the second is fused with the prelacunal to form a lacunolabial, and 9-13 sublabials (usually 10-12). Midbody, there are 20-27 rows of dorsal scales (usually 23-25). The ventrals number 170-216 (rarely 218) and the 51-71 subcaudals are mostly paired.

The color pattern is extremely variable, consisting of a dorsal ground color that may be tan, brown, gray, yellow, olive, or almost maroon. Midbody, this color is usually somewhat lighter than the head, anterior and posterior.

The dorsal ground color is overlaid with a series of pale-edged, dark brown subtriangular or trapezoidal markings on either side of the body, the apices of which reach the vertebral line. These marking may be situated opposite each other, or partially or completely juxtaposed; most specimens have a pattern with all three variations. In juveniles, the tip of the tail is white.

This species is often abundant within its range of southeastern Brazil, where it was responsible for 52% (3,446 cases) of snakebites between 1902 and 1945, with a 0.7% fatality rate (25 deaths).

The average venom yield is 25–26 milligrams (0.39–0.40 gr) with a maximum of 300 milligrams (4.6 gr) of dried venom. The venom is quite toxic. In mice, the median lethal dose (LD50) is 1.2-1.3 mg/kg intravenous, 1.4 mg/kg intraperitoneal and 3.0 mg/kg subcutaneous. For humans, the LD50 is estimated to be 210 milligrams (3.2 gr) subcutaneous.

Typical envenomation symptoms include local swelling, petechiae, bruising and blistering of the affected limb, spontaneous systemic bleeding of the gums and into the skin, subconjunctival hemorrhage and incoagulable blood. The systemic symptoms can potentially be fatal and may involve hemostatic disorders, intracranial hemorrhage, shock and renal failure.

"The drugs known as angiotensin converting enzyme (ACE) inhibitors, used for the treatment of hypertension and some types of congestive heart failure, were developed from a peptide found in the venom of this species."