(female on the left, male on the right)
Sexing these bugs is very difficult unless you catch them mating or egg-laying. Also, regional variations must always be considered.
Of the bugs in my area, I have noticed a few things:
1. - The body size of the females is about 2.5mm longer than the males.
2. - The females have two small spots on the apical sternite, on each side of the center-line, that I don't see on the males. (ventral)
Compare with the female here: ♀