The study of the number and position of setae (bristles, chaetae, hairs) on the insects in systematics. The number, shape and placement of many setae is of big importance during identification and often has systematic value as well.
When using setae while identifying specimens, it is recommended always to check both sides (left and right) in case setae are broken or lost altogether on the side examined firsts. Pinned material is prone to breakage but loss also may occur in living flies, especially on legs. The presence of an 'empty' alveolus may indicate a broke seta.
Links: http://www.ento.c.../fly.html#
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