Bill Gates once called the mosquito the deadliest animal on Earth, and this episode of the natural disasters series lays out why: the World Health Organisation estimates the insect kills roughly 750,000 people a year, far more than sharks, snakes, or any large predator. The film builds its case around two outbreaks. The first is the 2015-2016 Zika virus, which began in Brazil and spread across North and South America, tracked through footage of affected communities and public health responses. The second is a 2018 malaria outbreak spanning Thailand and Myanmar, where the parasite has grown resistant to standard drug treatments, making containment far harder for regional health workers. Interviews and archival footage trace how each disease moves from mosquito to human population and back, and how climate, travel, and drug resistance keep reshaping the threat. The episode's argument is blunt: the animal to fear is small, common, and already living near you.