Insects spread disease.
Malaria, which is a disease carried by Anopheles mosquitoes, kills over 1.5 million people in Africa every year, most of them children. Simulium flies in West Africa spread a disease to people called onchocerciasis which makes them go blind. If you swallow a flea in your house you run the risk of being infected with tapeworm. There are many other diseases transmitted between humans and between humans and animals by insects and in order to control the spread of these diseases we need to study the vector insects that spread them. Insects eat our crops.