Bothrops insularis, commonly known as the golden lancehead, is a highly venomous pit viper species found exclusively on the Ilha da Queimada Grande, off the coast of São Paulo state, in Brazil. The species is named for the light yellowish-brown color of its underside and for its head shape that is characteristic of the genus Bothrops. No subspecies of Bothrops insularis are currently recognized. It is one of the most venomous snakes in Latin America.
Physical morphology
Size and appearance
On average, B. insularis grows to a length of and , and it is known to reach . The color pattern consists of a pale yellowish-brown ground color, overlaid with a series of dorsal blotches that may be triangular or quadrangular, broad or narrow, and alternating or opposite along the dorsal median. In captivity, this yellowish color often becomes darker, which may be the result of poor circulation caused by ineffective thermoregulation. A banded pattern results when the pattern is opposite. The head lacks a well-defined post-orbital stripe. The belly is a uniform pale yellow or cream. The name "lancehead" refers to the distinctive head shape of all snakes in the genus Bothrops, which is somewhat elongated and comes to a point at the nose. B. insularis also has a longer tail than its closest relative, B. jararaca, which is most likely an adaptation to help the snake maneuver through the trees, and to eat larger prey like birds from a younger age.
Venom
Because of the isolated habitat of B. insularis, and the lack of mammal prey species, the venom of B. insularis has evolved to be adapted to the prey species of the island, primarily native ectotherms, arthropods and migrating birds. As a result, their venom is more potent towards these groups than mammals, and becomes more potent as the snake matures. Chemical analysis of the venom of B. insularis suggests that it is five times as potent as that of B. jararaca and is the fastest acting venom in the genus Bothrops.
Because B. insularis is only found in an area uninhabited by humans, there has never been an official report of a human being bitten by one, but other lanceheads are responsible for more human mortality than any other group of snakes in either North or South America. Ludwig Trutnau reports four human envenomations, three of which were fatal. The mortality rate for lancehead envenomations is 0.5–3% if the patient receives treatment and 7% if the patient does not receive treatment. The effects of envenomations by golden lanceheads include swelling, local pain, nausea and vomiting, blood blisters, bruising, blood in the vomit and urine, intestinal bleeding, kidney failure, hemorrhage in the brain and severe necrosis of muscular tissue.
Reproduction
Sexually mature Bothrops insularis mate during August and September, and have been known to mate both in the trees and on the ground. Like most vipers, B. insularis gives live birth to its young. The average size for a litter of golden lanceheads is 6.5 newborns. There are no published data for the size of the golden lancehead at birth, but they are probably of a similar size to Bothrops jararaca, which have a snout to vent length (SVL) of 24.5 to 25.3 cm (about 9¾ in) and a weight of 9.38 to 10.61 grams (about ⅓ ounce).
Owing to the dependence of B. insularis on migratory birds visiting the island as a food source, the reproductive cycle of female snakes has been suggested to be tied to seasonal bird migration patterns.
Geographic range
The species is endemic to Queimada Grande Island, Brazil, commonly known as Snake Island. Therefore, the type locality is the same: "Ilha da Queimada Grande, situado no litoral do Estado de S. Paulo, a cêrca de 40 milhas a S.O. da barra de Santos" (Brazil). This island has a total area of only 43 hectares or 430,000 square metres. Travel to the island is strictly prohibited by the Brazilian government.
Habitat
The island of Queimada Grande is what is classified as "subtropical" or "tropical moist forest". The coordinates for the island are . The island contains several different kinds of habitat including forest, clearings, and shrubs. The island has a very mild climate; the temperature never falls below 18 degrees Celsius, and at its hottest is just over 22 degrees Celsius (64 to 72 °F). Because of the extremely rocky terrain and the isolation of the island, however, the island is not easily accessible and is not populated by humans, or for that matter, any other mammal. The quality of its habitat continues to decline due to vegetation removal by members of the Brazilian Navy who maintain the lighthouse on the island.