the curved hairs on emarginated male wing of C. acutangula (note: also discal cell is modified due to this emargination) serve during copulation to better hold the female wing; in other sphaerocerids the male mid leg is often modified for the same purpose (combs of curved setae or spines on tibiae and femora, curved tibia, see extreme case - Limosina silvatica), also the ventral hook on hind femur in Crumomyia nitida may serve similarly. There are also vice-versa modifications, e.g. in Phthitia empirica the 2nd costa sector (Cs2) of female wing is modified because the male holds by its armed middle legs the female wings just in Cs2.