Eggs

Mosquito eggs are usually 1 mm or less in length. Eggs are laid on the surface of the water, either individually (e.g. Anopheles) or in rafts (e.g. Culex), or in sites subject to inundation by rain water (e.g. Psorophora). In the latter case the eggs hatch when flooded.

The shell, or chorion, of the mosquito egg is formed of two principal layers, an opaque inner chorion and a transparent outer chorion. In newly laid eggs, the inner chorion is also transparent, thus the eggs are white when laid and gradually become dark brown or black. The anterior end of the egg (the end opposite the head of the developing larva) bears the micropylar disc surrounding a minute opening, the micropyle, which permits the spermatozoa to enter during oviposition. The eggs of culicine mosquitoes are usually elongate-oval in shape. The shape of the eggs is generally characteristic of the various genera. The pattern of impressed and raised markings on the outer chorion provides useful taxonomic characters. The eggs of anopheline mosquitoes are generally boat-shaped. Dorsally, the outer chorion is modified to form a projecting frill, which partly or completely surrounds a flattened deck, and a pair of hollow lateral floats. Variations of these structures, along with the lobed tubercles at either end of the deck, provide characters for distinguishing closely related species.