You could pull its wings off. If it cries like a baby, it's male. If it winces whilst carrying on with the ironing whilst simultaneously making multiple meals to put in the freezer, it's female.
First catch a fly. But be careful you don't hurt her/him. Now tie the fly. You have to very careful wile undressing the fly. You have to wear a mask to hide your identity. If it's male- OK. But if it's female she might shout so on a precautionary measure tie the mouth as well. As soon as the underwear goes down, you can see what's there. And there you go, mission accomplished!!!!! Kudos :)