Subcosta

The subcosta (Sc) is a major longitudinal wing vein in many insects. It lies just behind the leading-edge costa (C) and extends from the wing base toward the apex, where in many species it terminates or fuses with other veins. Sc is often accompanied by cross-veins that connect it to neighboring veins, helping to reinforce the wing's structural network.

Across insect groups, the subcosta shows substantial variation. In some taxa it remains a distinct, well-developed vein along much of the wing; in others it is shortened, reduced, or completely fused with the radius (R) or even absent as a separate structure. This variation is common in groups such as Odonata, Lepidoptera, and Diptera and is frequently interpreted in a phylogenetic context, as the pattern of Sc (presence, absence, and connections) reflects evolutionary changes in wing design and flight style.

Function and significance: The subcosta contributes to wing rigidity and load distribution during flight and is a key feature used in wing venation-based taxonomy. Its local modifications—such as loss, fusion, or branching—are important characters in distinguishing taxa, both extant and fossil. The term subcosta is derived from Latin subcosta, meaning "under the rib."