A species of chameleon that spends most of its short life as an egg has been discovered by conservationists in Madagascar. The unusual reptile, known as Labord's chameleon, develops inside an egg for up to nine months, but after hatching lives only a few months longer, during which it rapidly matures, mates and dies.

Because the chameleons all hatch at the same time, the entire population is the same age, apart from a very brief period when adults are still alive after laying their eggs. The life cycle is more akin to that of insects than reptiles or any other four-legged vertebrate, researchers said.

Kristopher Karsten, a zoologist at Oklahoma State University, working with scientists in Madagascar and at the American Museum of Natural History in New York, discovered the reptile's unusual lifestyle during field studies over five seasons in the arid south-west of the island.

Hatchlings emerged at the beginning of the rainy season, around November, and reached sexual maturity within two months. By the beginning of February the chameleons had already started to show signs of old age, becoming slower, losing weight and occasionally falling out of trees because their grip had weakened. Some were found dead on the forest floor from unknown causes.

Writing in the US journal Proceedings of the National Academy of Sciences, the team says the animal may have compressed its lifespan to cope with extremes of weather in Madagascar. "The notorious rapid death of chameleons in captivity may, for some species, actually represent the natural adult life span," they said.