Jararaca

Identification

The jararaca is a lancehead pit viper with a flat, sharply ridged head and a heat-sensing pit on each side of the face between the eye and the nostril³. Its colour varies with the local soil and can be olive, brown, grey, tan, yellowish or reddish³. Dark brown triangular or trapezoid marks, edged with paler colour, run along both sides of the body, and a dark stripe runs from behind the eye towards the jaw³. Young snakes often have a pale tail tip^2,3.

In one museum sample, the ten largest of 29 jararacas averaged 1.06 m long². Females grow larger than males, and individuals up to 1.6 m have been reported³.

Distribution

The jararaca lives in eastern and southern Brazil, from southern Bahia south through Espírito Santo, Rio de Janeiro, Minas Gerais, São Paulo, Paraná and Santa Catarina to Rio Grande do Sul, and west to eastern Mato Grosso¹. It also occurs in north-eastern Paraguay and in Misiones province, Argentina¹. It is mainly a snake of the Atlantic Forest, found from sea level to about 1,000 m^2,3.

Habitat

The jararaca prefers dense evergreen and deciduous forest in the Atlantic Forest, but it is also found in scrub, upland forest and farmland near cover³. It is semi-arboreal: adults mostly stay on the ground, while young snakes are found more often on low vegetation^2,3.

Behaviour

The jararaca is mostly found at night, coiled in an ambush position³. It is much less active in the colder months and most active in the warm, rainy season³. When threatened it may vibrate its tail, raise its head and neck, thrash its body or strike, and it may also hide its head or flatten its body³. Its colours blend with the ground, which helps it avoid predators such as white-eared opossums³.

Diet

The jararaca is a sit-and-wait hunter that eats a wide range of prey². Of 45 prey items found in preserved specimens, 71% were mammals, 18% frogs, 7% birds, and the rest centipedes and lizards². Young jararacas eat mostly frogs and lizards, which they attract by wriggling their pale tail tip like a small grub, while adults switch mainly to rodents^2,3. Rodents are usually bitten, released and then tracked down, while frogs are held until they die².

Reproduction

The jararaca gives birth to live young¹. Mating takes place in April and May, but females store sperm and fertilisation happens months later, in spring³. The young are born mainly from February to April, with about 10 to 14 in a litter³. Newborns are about 24–28 cm from snout to vent and weigh 6–9 g³.

Venom and medical significance

The jararaca is highly venomous, and the WHO places it in Category 1, the highest medical importance, in Brazil⁴. Lanceheads cause about two-thirds of all reported snakebites in Brazil, and the jararaca was the main species in a hospital trial of lancehead bites in São Paulo^7,8. A bite causes pain and swelling, sometimes with bruising and bleeding from the bite, gums, skin or urine; complications can include serious bleeding, infection, tissue death at the bite and kidney failure⁵. It is treated with antibothropic antivenom, given in hospital⁶, and in the São Paulo trial no patients died, though some developed abscesses or tissue damage⁸. Research on jararaca venom also led to captopril, the first drug of its kind to block the enzyme ACE, now used worldwide to treat high blood pressure⁹. Anyone bitten should go to hospital immediately.

Conservation

The jararaca is listed as Least Concern on the IUCN Red List (published 2019)¹⁰. It is abundant in much of its range, and its habitats include farmland, which is one reason people meet it often³. Much of its Atlantic Forest home has been broken up into fragments³.

Similar species

In Brazil, the South American rattlesnake (Crotalus durissus) is also a dangerous pit viper, but it has a rattle on its tail¹¹. Rattles can break off or be lost, however¹². The jararaca is smaller and lighter than the jararacuçu (Bothrops jararacussu), and it differs from the Brazilian lancehead (Bothrops moojeni) by being smaller, having a wider stripe behind the eye and lacking a wavy mark on the nape³. These differences are not a safe basis for handling any snake. Keep your distance from every snake you cannot identify.

In captivity

The jararaca is a dangerously venomous snake and is not suitable as a pet. In Brazil, keeping venomous snakes is allowed only in research centres or for the pharmaceutical industry¹². At the Instituto Butantan, jararacas are kept to supply venom for antivenom production, and each produces an average of about 83 mg of dried venom¹³.