Science: Queer Vipers

The island of Queimada Grande, off the coast of southeastern Brazil, is the kingdom of a snake called Bothrops insularis. Pit vipers related to rattlesnakes but much more poisonous, they swarm in the undergrowth, festoon the trees. They are found nowhere else in all the world, and their control of the mile-long island has not been contested since 1921, when the Brazilian government withdrew its lighthouse keepers after snakes had killed three of them and the wife of a fourth. They seem to live an ideal life, with plenty of sea birds to prey upon and no enemies. But all is not well in their paradise. Last week Herpetologist Alphonse Richard Hoge of São Paulo’s Butantan Institute of serum therapy reported that the snakes were producing more and more offspring that were neither male nor female, but hermaphrodites.

In 1952 Dr. Hoge collected 164 Bothrops on the island. An assistant dissecting one of them showed him what he thought was a tumor. “That’s no tumor,” said Hoge. “That’s an atrophied embryo.” The assistant replied: “It can’t be; it came from a male.” Both Hoge and the assistant were right; the snake had well-developed male reproductive organs but also female ovaries. Hoge checked his specimens and found that more than half were hermaphrodites. Only 15 were true females, and all of them were sterile. The hermaphrodites are bigger than either true males or females. Most are more female than male, and are capable of bearing young.

Most species breed out serious aberrations like hermaphroditism, but this is not happening in the case of Bothrops insularis. When Dr. Hoge examined pickled specimens collected before World War II, he found a much bigger proportion of normal individuals. Recently, Dr. Hoge went back and collected 68 fresh snakes on the island, plans to coop them up together in pairs in all possible combinations to see whether pairs of hermaphrodites can reproduce without male participation. However they reproduce, the hermaphrodites are comparatively infertile, produce only four to six embryos v. the 20 to 24 of mainland vipers. “In my opinion,” says Dr. Hoge, “Bothrops insularis will breed itself into increasing abnormality, decreasing fertility and eventual extinction.”