These glands are represented externally by a special plate, the cribellum, which lies in front of the ordinary spinning mamillae, and by a comb of short bristles, the calamistrum, placed in the penultimate segment of the left of the last pair.
An ear of another type is found in the swollen second segment of the feeler in many male gnats and midges, the cuticle between this segment and the third forming an annular drum which is connected with numerous nerveendings, while the fine bristles on the more distal segments vibrate in response to the note produced by the humming of the female.
Some of the species of Aviculariidae also appear to be warningly coloured with black or black and red, and their coloration is associated with the urticating nature of their bristles, which makes them highly unpalatable to vertebrate foes.
Thus in Lithospermum the nutlets are hard like a stone, in Myosotis usually polished, in Cynoglossum covered with bristles, &c.
The latter again are divided into Metanopsilae (in which the metanotum or posterior region of the thorax is bare) and Metanotrichae (in which the metanoturn is clothed with bristles or scales).