Jararacussu

Fascinating facts about the Jararacussu

• A jararacussu can grow up to 2.2 m (7.2 ft) and has fangs 2.5 cm long.
• When a jararacussu gives birth, it releases a litter of 16 to 20 newborns during the rainy season.
• In a study of 29 bites in São Paulo, victims bitten by snakes longer than 50 cm showed severe necrosis, shock and kidney failure, while smaller snakes more often caused blood that wouldn’t clot at all.
• The venom’s LD₅₀ values are startling: just 0.14 mg per kilogram intravenously can be lethal, and a single snake can pump out about 1000 mg – enough to kill roughly 10,163 rats in one go.
• Three patients aged 3, 11 and 65 died from respiratory and circulatory collapse despite receiving antivenom in intensive care, underscoring how quickly this pit viper’s cocktail of cytotoxins, hemotoxins and myotoxins can shut down vital systems.

At a glance

About the Jararacussu

The jararacussu, Bothrops jararacussu, is a formidable pit viper that can reach up to 2.2 metres (7.2 ft) in length, its robust body capped by a broad head and medium-sized eyes with vertical, elliptical pupils. Its dorsal scales are heavily keeled, and its coloration ranges from deep brown to almost black or bright yellow, marked by a series of dark arches and X-shaped spots along the midline. When it unfurls its 2.5 cm fangs, it can deliver a venom load of roughly 1 000 mg, enough to kill more than ten thousand rats, making it one of the most dreaded snakes in South America. The snake’s behavior is aggressively opportunistic; it basks in the morning sun, then roams both day and night to hunt amphibians and rodents, often along river banks, low swampy regions, and the understory of Atlantic and semi-deciduous forests. A surprising trait is its ovoviviparous reproduction: in the rainy season a single female gives birth to 16-20 neonates, which emerge fully formed and ready to hunt. Endemic to coastal Brazil, from Bahia to Santa Catarina, Paraguay, southeastern Bolivia, and northeastern Argentina’s Misiones Province, the jararacussu thrives in a mosaic of habitats, from perennial and pine forests in Paraná to swampy lowlands. Its venom, a cocktail of cytotoxins, hemotoxins and myotoxins, has caused severe clinical cases: a study of 29 bites in São Paulo recorded necrosis, coagulopathy, kidney failure and three deaths, underscoring the snake’s medical significance and the urgent need for effective antivenom treatment. Yet despite its lethal reputation, the species remains a vivid thread in the fabric of South America’s forest ecosystems, silently shaping prey populations and serving as a reminder of nature’s raw power.

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