The use of insects for warfare may have been attempted in the Middle Ages or earlier , but was first systematically researched by several nations during the twentieth century . It was put into practice by the Japanese army 's Unit 731 in attacks on China during the Second World War , killing almost 500,000 Chinese people with fleas infected with plague and flies infected with cholera . Also in the Second World War , the Germans explored the use of Colorado beetles to destroy enemy potato crops . During the Cold War , the US Army considered using yellow fever mosquitoes to attack Soviet cities
Unit 731
Unit 731
Human interactions with insects