Mosquitoes are common, flying insects that live in most parts of the world. Over 3,500 types of mosquitoes can be found worldwide. Some mosquitoes can be vectors. A vector is an animal, insect, or tick that spreads pathogens (germs) to people and animals. The germs (viruses and parasites) that mosquitoes spread can make you sick. Some mosquitoes bite, but do not spread germs. These types of mosquitoes are called nuisance mosquitoes.