There are 161 different families of true flies (of the order Diptera) in the world and these make up about 10% of all named animals. The Ceratopogonidae or biting midges are one of the most speciose families in the order, with over 6,200 named species. How can they be recognized? There are four different life stages that differ tremendously from one another: the egg, larval, pupal and adult stages. To really get to know them, one needs a dissecting microscope and a good light.
Adult biting midges share the following features which distinguish them from nearly all other flies: they tend to be small with a wing length of 1-6 mm, the wing has one or two radial vein branches reaching the wing margin (Leptoconops has a weak third radial vein) and has two median vein branches (posterior one may be weak); the postnotum lacks a median longitudinal groove, the antenna usually has 13 flagellomeres (some have less), and most females have biting mouthparts (the mandibles are serrate); some species have females which do not feed and therefore have simple mouthparts. In the field, most adults can be recognized by the wings overlapping each other over the abdomen (when not flying, of course!) and the presence of front legs that are shorter than the hindlegs; this is not fool proof as the features are shared by some non-biting midges in the family Chironomidae and some Ceratopogonidae (some Stilobezzia) do not have overlapping wings. After sweeping with an insect net, adults tend to crawl slowly up the side of the net from the bottom debris/ and other insects. These are useful tools when collecting adults with relatively few exceptions.
The pupae are difficult to separate from those of some other families but all have the following characteristics: the well-developed respiratory organs are each a single, undivided structure (not bifurcating), the third leg is curled under the wing sheath, with only the tip protruding in most, the apex of the abdomen is more or less straight (not curled under the thorax) and they have two pointed anal processes (never a paddle), the pupae is not enclosed in a silk tube, and the pupae are not very active: the most they can do is to move their abdomens lazily in slow circular motions.
The larvae are relatively easy to recognize. They are the only fly larvae in which there is a head capsule, no open spiracles and with a well-developed pharyngeal complex in the head (a large ‘mortar and pestle’ apparatus to grind food shortly after it is swallowed). The larvae of most genera are very active swimmers, with a characteristic lashing movement that, once seen, is distinctive. However, there are other biting midges that are quite different, semi-aquatic or terrestrial; these are also distinctive and Andy Murray has some remarkable photos and videos of these. The eggs of Ceratopogonidae cannot be recognized as a group but a few have really distinctive egg shapes. For example, all Dasyhelea have C- shaped eggs and those of the Stenoxenini have a frill at one end. Many ceratopogonids have very narrow and elongate eggs which are distinctive from those of other flies.
For those with the knowledge and skills, keys to adults and pupae are available to at least the generic level (there are 108 genera) in various publications (see “Classification and Identification”. To properly prepare material for study, check out the section below “How to Capture and Study Biting Midges”.