Giant tortoises on the Galapagos Islands could be at risk from mosquitoes that have developed a taste for reptile blood.
Scientists are worried people visiting the islands in the Pacific Ocean could bring mosquitoes carrying diseases like malaria with them by mistake.
Local mosquitoes, which feed on the reptiles, could then pick up the diseases and pass them on.
The tortoises are not immune to malaria because the islands are very isolated.
Planes flying into the Galapagos Islands have to be sprayed with insecticide to try to prevent infected mosquitoes being transported to the islands.
The Galapagos Islands are home to some of our rarest species of plants and animals, including giant tortoises, marine iguanas and rare sea lions.
The giant tortoises have grown so big because they have no natural predators.
The islands are 1,000km off the coast of Ecuador in South America and they were the first place on the planet to become a protected World Heritage site more than 30 years ago.