Certain insect species are the carriers of some of humanity's most dreaded diseases, including malaria, typhus, and plague. As consumers of agricultural crops and parasites of our livestock, insects are also humankind's number one competitor for resources.
Mosquitoes, are the most notorious carriers, or vectors, of disease and parasites. Female mosquitoes rely on warm-blooded hosts to serve as a blood meal to nourish their eggs. During the process of penetrating a host's skin with their long, sucking mouth parts, saliva from the mosquito is transferred into the bite area. Any viral, protozoan, or helminth infections carried in the biting mosquito can be transferred directly into the blood stream of its host. Among these are malaria, yellow fever, W. bancrofti (filariasis and elephantiasis), and D. immitis (heartworm).
Flies also harbor diseases that can be transmitted to humans and other mammals when they bite to obtain a blood meal for themselves. For example, black flies can carry river blindness, sandflies can carry leishmaniasis and kala-azar, and tsetse flies (found mainly in Africa), carry the trypanosomes that cause sleeping sickness. Livestock, such as horses and cattle, can be infected with a variety of botflies and warbles that can infest and feed on the skin, throat, nasal passages and stomachs of their hosts.
Fleas and lice are two of the most common and irritating parasitic insects of humans and our livestock. Lice commonly live among the hairs of their hosts, feeding on blood. Some species are carriers of the epidemic inducing typhus fever. Fleas usually infest birds and mammals, and can feed on humans when they are transferred from pets or livestock. Fleas are known to carry a variety of devastating diseases, including the plague.