An insect's wing venation is an important morphological feature for placing it in the correct family or genus. You will need to know the names of the different wing veins in order to identify many insects accurately, using a dichotomous or descriptive key.
Most entomologists use the wing venation system represented in this diagram, which was devised by John Comstock and George Needham in the late 1890's. Comstock and Needham named each of the 6-8 longitudinal veins, as well as the crossveins, on a hypothetical insect wing. These names remain the standard terminology used to describe wing features today.
The longitudinal veins are always named in the following order, beginning with the leading edge of the wing and working toward the trailing edge:
- C – costa - the vein along the leading edge of the wing
- SC – subcosta - the second longitudinal vein
- R – radius - the third longitudinal vein
- M – media - the fourth longitudinal vein
- CU – cubitus - the fifth longitudinal vein
- A – anal - the remaining veins between the cubitus and the trailing edge of the wing
With the exception of the costa and anal veins, longitudinal veins may be branched, and are then numbered, beginning with the anterior branch and moving to the posterior branch. The subcosta vein (SC) can be branched once; the two branches are then labeled SC1 and SC2. The radius is more complex. The first posterior branch is called the radial sector (RS), and this may, in turn, be forked twice. The anterior radius is then labeled R1, and each of the forks of the radial sector are numbered R2, R3, R4, and R5. The media may also be forked twice, with the veins reaching the wing margin. They are labeled M1, M2, M3, and M4. The cubitus may branch into two parts, CU1 and CU2. In some cases, the anterior branch may again be divided into CU1a and CU1b. Finally, there may be as many as four unbranched anal veins, each with its own label, A1, A2, A3, and A4.
The crossveins connect the longitudinal veins, and are typically named for the two veins which they connect:
- c-sc* - crossvein connecting the costa and subcosta
- r - crossvein connecting adjacent branches of the radius
- r-s* - crossvein connecting the subcosta and radius
- r-m - crossvein connecting the radius and media
- m - crossvein connecting adjacent branches of the media
- m-cu - crossvein connecting the media and cubitus
- cu-a - crossvein connecting the cubitus and the first anal vein
Certain additional crossveins have special names:
- h – humeral - this crossvein connects the costa and subcosta near the base of the wing
- s – sectorial - a crossvein that connects either the radius (R1) to the branch R4-R5, or connects R3 to R4
* - These veins are not represented on the diagram.