These stridulating organs were mentioned by C. Darwin as probable examples of the action of sexual selection; they are, however, frequently present in both sexes, and in some families also in the larvae.
In a large number of beetles of different families, stridulating areas occur on various segments of the abdomen, and are scraped by the elytra.
Stridulating organs among beetle-larvae have been noted, especially in the wood-feeding grub of the stag-beetles (Lucanidae) and their allies the Passalidae, and in the dung-eating grubs of the dor-beetles (Geotrupes), which belong to the chafer family (Scarabaeidae).
Whatever may be the true explanation of stridulating organs in adult beetles, sexual selection can have had nothing to do with the presence of these highly-developed larval structures.
The root-feeding larvae of the cockchafer and allied members of the Scarabaeidae have a ridged area on the mandible, which is scraped by teeth on the maxillae, apparently forming a stridulating organ.
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