to tell which gender is not that puzzling anyway...

flies can be easily distinguished...
and to tell you...
i've been a flies expert till all these years...

my parameter is very simple... you too can make this... and determine which fly gender is...

just place earthworms on the tabletop...

if the fly landed to a male earthworm... that's a female flies...

if the fly landed to a female earthworm... that's a male flies... :D