Adults

Adult mosquitoes are usually 3-6 mm long, but some toxorhynchitines, which are the largest mosquitoes, are nearly 20 mm long. As in other insects the body has three principal regions, the head, thorax and abdomen. The head is the anterior section of the body bearing the compound eyes, antennae and mouthparts. It is separated from the second or intermediate division of the body, the thorax, by a membranous tube called the cervix, or neck. The thorax is comprised of three segments, each bearing a pair of legs. The largest or middle segment of the thorax bears the wings and the reduced third or posterior segment bears the halteres. The abdomen is the third, posterior division of the body. It consists of ten segments and the terminal genital structures involved in reproduction. The male genitalia are extremely important in species identification in most genera. Except for sclerotized elements of the alimentary canal and the reproductive system, the internal anatomy is not used in mosquito taxonomy. The presence or absence of setae and the placement and color of scales provide important characters for species identification.

Mosquitoes are much more extensively clothed with scales than other Diptera which have scales. The scales are either pale or dark. Dark-colored scales vary from reddish brown to black depending on the species and to a lesser extent on the age of the specimen. Some mosquitoes have metallic-colored scales which appear blue, green, gold, red or violet in certain light. Pale-colored scales are white, silver, yellow or gold. Scales may be broad and flat, narrow and curved, or erect and forked apically; those comprising the wing fringe are fusiform in shape. Scales are easily rubbed from the body; hence, important taxonomic characters may be missing in rubbed specimens. The color of the integument also varies interspecifically, and this may influence the overall color of the scales.