Tityus serrulatus

Tityus serrulatus, commonly known as the Brazilian yellow scorpion, belongs to the Buthidae family. This species is endemic to Brazil and produces a highly potent venom. It is considered the most hazardous scorpion in South America and accounts for the highest number of fatal stings.

Adults usually reach 5 to 7 centimeters in length. Their pale-yellow legs and pedipalps contrast with a darker yellowish-brown trunk and tips of the limbs and tail. Like other Buthidae, they have a bulbous, segmented tail often carried curved forward over the back, marked by prominent ridges and serrations. The tail ends in a venomous barb used to immobilize prey or for defense.

The scorpion is found across much of Brazil, including the states of Alagoas, Bahia, Ceará, Espírito Santo, Goiás, Mato Grosso, Mato Grosso do Sul, Minas Gerais, Paraná, Pernambuco, Rio de Janeiro, Rio Grande do Norte, Rio Grande do Sul, Rondônia, Santa Catarina, São Paulo, Sergipe, and the Federal District. According to scientist Rogério Bertani of the Butantan Institute, deforestation and urban growth are increasing the species' presence, and he believes the problem will worsen. By 2018, a notable rise in urban populations of T. serrulatus in São Paulo had occurred, linked to abundant prey like cockroaches, available shelter, and few predators. Reported scorpion stings in Brazil jumped from 12,000 in 2000 to 140,000 by 2018.

Its diet consists of insects such as cockroaches, and it thrives in sewers and trash heaps. A low metabolic rate allows it to survive months without food. The species is usually parthenogenetic.

Scorpions cause more human envenomations in Brazil than all other venomous animals combined, including snakes and spiders. Mortality rates among children and the elderly range from 1.0 to 2.0%, and T. serrulatus is responsible for more medically significant accidents than any other scorpion in the country. Most stings happen in urban areas, inside or near homes, with higher frequency in the south and southeast during warm, rainy months; seasonal variation is minimal in the north, northeast, and center-west.

Mild cases primarily involve localized pain. The venom contains TsIV, which slows sodium channel inactivation in muscles and nerves. An excitatory neurotoxin attacks the autonomic nervous system, triggering release of adrenaline, noradrenaline, and acetylcholine. Symptoms may include hyperglycemia, fever, priapism, agitation, hypersalivation, tachycardia, hypertension, mydriasis, sweating, hyperthermia, tremors, gastrointestinal issues (diarrhea, abdominal pain, nausea, vomiting), and pancreatitis. Convulsions and coma are rare but possible. Death typically results from pulmonary edema and cardiorespiratory failure, occurring within 1 to 6 hours or 12 to 14 hours, depending on age, health, and venom dose. Venom lethality varies by region: T. serrulatus from the Federal District has an LD50 of 51.6 μg/kg, while those from Minas Gerais have an LD50 of 26 μg/kg. A nationwide study from 2000 to 2012 recorded 482,616 scorpion accidents and 728 deaths in Brazil, all fatal cases attributed to the genus Tityus, with T. serrulatus believed responsible for the vast majority.