World Mosquito Day is celebrated every year on August 20 and the day is dedicated to a vital discovery by a British doctor, Sir Ronald Ross in 1897. The important discovery said that it was the "female mosquitoes transmit malaria between humans". To commemorate the day, every year the London School of Hygiene and Tropical Medicine celebrates the day as World Mosquito Day. Watch the video to find out more about the world’s deadliest killers.