Coloured scanning electron micrograph (SEM) of Western yellowjacket wasp wing hooks(Vespula pensylvanica). Yellow jacket wasps are members of the order Hymenoptera (meaning membranous wings). Yellow jackets have four wings, but they often are thought to have just two because a hook apparatus attaches the small rear wings to the forewings, making them appear as one. These hooks, called hamuli, appear in a row on the rear wing and catch on to a ridge on the lower margin of the forewing. Hamuli are characteristic of advanced insects and are an adaptation that ensures well-controlled, rapid flight. The number of hamuli per millimetre of wing length is characteristic of insect caste. Wings of workers have more numerous hamuli, which corresponds with specialization for foraging or carrying loads in flight. Hamuli allow both wings operate in unison to form a single aerodynamic surface. Magnification: x70 when shortest axis printed at 25.
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