Mosquitoes (alternate spelling mosquitos) are a group of about 3500 species of small insects that are flies (order Diptera). Within Diptera they constitute the family Culicidae (from the Latin culex meaning “gnat”). The word “mosquito” (formed by mosca and diminutive -ito) is Spanish for “little fly”. Mosquitoes have a slender segmented body, a pair of wings, three pairs of long hair-like legs, feathery antennae, and elongated mouthparts.
Mosquitoes first appeared about 226 million years ago. Fossils of primitive mosquitoes have been found that are over 90 million years old; fossils similar to modern mosquitoes, 79 million years old; fossils identical to modern mosquitoes, 46 million years old. The life cycle consists of the egg, larva, pupa, and adult. Eggs are laid on the water surface; they hatch into motile larvae which feed on aquatic algae and organic material.
A female of most species has tube-like mouthparts (called a proboscis) which can pierce the skin of a host (colloquially but incorrectly referred to as a “bite”) and imbibe blood, which contains protein and iron needed to produce eggs. Thousands of mosquito species feed on the blood of various hosts — vertebrates, including mammals, birds, reptiles, amphibians, and some fish; and some invertebrates, primarily other arthropods. This loss of blood is seldom of any importance to the host.
The saliva of the mosquito transmitted to the host with the bite can cause itching and a rash. In addition, many species of mosquitoes inject or ingest (or both) disease-causing organisms with the bite and are thus vectors of diseases such as malaria, yellow fever, Chikungunya, West Nile virus, dengue fever, filariasis, Zika virus and other arboviruses. By transmitting diseases, mosquitoes kill more people than any other animal taxon: over 700,000 each year.
The oldest known mosquito with an anatomy similar to modern species was found in 79-million-year-old Canadian amber from the Cretaceous. An older sister species with more primitive features was found in Burmese amber that is 90 to 100 million years old. Two mosquito fossils have been found that show very little morphological change in modern mosquitoes against their counterpart from 46 million years ago. These fossils are also the oldest ever found to have blood preserved within their abdomens.