The World's Most Dangerous Insects

The tsetse fly looks similar to an ordinary house fly, but unlike its harmless twin, it can transmit a number of different diseases to humans, including human African trypanosomiasis, also known as sleeping sickness. And unlike the mosquito, which can bite without you even noticing, according to the BBC, "the tsetse fly's mouth has tiny serrations on it that saw into your skin on its way to suck out your blood," leaving it with a particularly painful bite.

Sleeping sickness is significantly less deadly than it used to be, and in 2020, Togo became the first country in Africa to eliminate sleeping sickness as a public health problem. In 2015, there were fewer than 3,000 cases across the African continent, and in 2018, that number dropped to 977, according to the World Health Organization.

Tsetse flies carry Trypanosoma brucei rhodesiense, the parasite that causes sleeping sickness, and they can transmit it to other animals in addition to humans. Animal trypanosomiasis, also known as nagana in cattle or sura in horses, is considered a "major livestock production and public health constraint," writes BMC Veterinary Research.

The symptoms of sleeping sickness is similar in both animals and humans. After an initial fever and muscle aches, the infected person becomes more and more tired. "Personality changes, severe confusion, and poor coordination can also happen." Without treatment, it can be deadly. From 1900 to 1920, over 250,000 people died from sleeping sickness in Uganda alone.