A species is considered extinct when the last living individual has died. Proving that a species is extinct is not always straightforward. Many scientists rely on guidelines set forth by the International Union for Conservation of Nature (IUCN) on when to declare a species extinct.
These guidelines involve repeated surveys of the specie’s known habitat until “there is no reasonable doubt that the last individual has died.” Despite the best efforts to verify that a species is truly gone, there are instances of where after even decades of no observations, a species is found to still be extant.
Fernandina Island Galápagos Tortoise
Recently, two formerly extinct species were separately discovered to still be living. The Fernandina Island Galápagos tortoise, until a female individual was likely discovered in February 2019, had last been seen on the island over 100 years ago in 1909. DNA testing will need to be done to verify the discovery. More: How an ‘extinct’ tortoise was rediscovered after a century – National Geographic
Wallace’s giant bee (Megachile pluto)
The Wallace’s giant bee (Megachile pluto) made its second rediscovery from extinction by a team of biologists exploring the islands in the North Moluccas, Indonesia in January of 2019. While on one of the islands, the biologists discovered a female individual which made its test within a termite mound.
The bee gets its name from British explorer and naturalist Alfred Russel Wallace who discovered it in 1859. Prior to the 2019 discovery, the bee had last been seen in 1981 by American researcher Adam Catton Messer.
Prior to 1981, the bee had been considered extinct. Since the 1981 sighting, the bee had not been observed for almost four decades, prompting scientists to fear it was extinct. More: Rediscovering Wallace’s Giant Bee: In Search Of Raja Ofu, The King Of Bees – Global Wildlife Conservation