In insect anatomy the arista is a simple or variously modified apical or subapical bristle, arising from the third antennal segment. It is the evolutionary remains of antennal segments, and may sometimes show signs of segmentation. These segments are called aristameres.
The arista may be bare, sometime appearing no more than a simple bristle, pubescent - covered in short hairs, or plumose - covered in long hairs.
The presence of an arista is a feature of the DipterasuborderBrachycera and may be especially well-developed in some species. It is known to contain thermo and hygroreceptors in Diptera that helps the flies to detect changes in temperature and moisture.