Makes a Biting Midge a Biting Midge?
There are 136 different families of flies in the world http://www.sel.barc.usda.gov/Diptera/names/famlista.htm and 82 of these occur in Costa Rica. One of these families are the Ceratopogonidae or biting midges (purrujas). How can they be recognized? There are four different life stages that differ tremendously from one another: the egg, larval, pupal and adult stages. 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 nearly all females have biting mouthparts (the mandibles are serrate); a few 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. Nevertheless, these are useful tools when collecting adults. 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, the apex of the abdomen is more or less straight (not curled under the thorax) and has two pointed anal processes (never a paddle), the pupae is not enclosed in a silk tube (at most a poorly developed silk tube in which the abdomen is loosely encased), and the pupae are not very active: the most they can do is to move their abdomens in slow circular motions. The larvae are rather 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 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, a tentative key to adults to the level is available in the section "Key to the Genera of Adult Ceratopogonidae in Costa Rica". To properly prepare material for study, check out the section below "How to Capture and Study Biting Midges". Knowledge of body parts is also necessary to use the key and studying the Morphology and Ceratopogonidae chapters in the "Manual of Nearctic Diptera" will provide the proper tools to do so; however, I have tried to illustrate the key in some detail, which should help those who are less experienced.