Wing coupling

Some four-winged insect orders, such as the Lepidoptera, have developed a wide variety of morphological wing coupling mechanisms in the imago which render these taxa as "functionally dipterous" (effectively two-winged) for efficient insect flight.

[3] The more primitive groups of moth have an enlarged lobe-like area near the basal posterior margin, i.e. at the base of the forewing, called jugum, that folds under the hindwing in flight.

Along with the frenulum, a spine at the base of the forward or costal edge of the hindwing, it forms a coupling mechanism for the front and rear wings of the moth.

In the butterflies[a] and in the Bombycoidea[b], there is no arrangement of frenulum and retinaculum to couple the wings.

Despite the absence of a specific mechanical connection, the wings overlap and operate in phase.