Count the abdomen segment it is 6 for female and 8 for male. Or you could count the 'spike' on the underside of her abdomen, 6 for male and 5 for female. Male will also develop thicker antenna compare to female. Adult male has feathery antenna.
If you could post the latest pic of your B. mendica (abdomen shot) that would help.
That is helpful. I'm starting to think they are both males. I'm going to let b mendica hang for a bit since it just molted and then take more pics. Should be easier to tell today being a little bigger.