Johnston's Organ

Johnston's organ is a collection of sensory cells found in the pedicel (the second segment) of the antennae in the Class Insecta. Johnston's organ detects motion in the flagellum (third and typically final antennal segment). It consists of over 200 scolopidia arrayed in a bowl shape, each of which contains a mechanosensory chordotonal neuron. The presence of Johnston's organ is a defining characteristic which separates the Class Insecta from the other hexapods belonging to the group Entognatha.

Johnston's organ can be seen in Drosophila. It consists of a sail-like flagellum which rotates in a structure called the funiculus. Air movement deforms the cuticle at the joint between segments 2 and 3 where the sensory units of Johnston’s organ attach. Johnston's organ reacts between 150 and 500 Hz. One function is for detecting the wing beat frequency of a mate. The third segment can also be deformed by gravity irrespective of head orientation and this enables it to sense gravity.

Johnston's organ was named after the physician Christopher Johnston, father of the physician and Assyriologist Christopher Johnston.

Johnston's organ can also sense wind.