Just from observation of eggs and sperms.
I have been looking very closely at my Malu, Mag, Haddoni and Gigantea to see if I can see any structure differences between various animals, but not able to see any significant differences. I am sure if we ant to dissect them we can tell male from female but I am not to the point of killing them yet.
I was trying to see the difference between my female and male Malu, but the female died before I can make any significant observation.