Are you sure you're looking at females? Females have a swollen stem behind the flower and it has a different shape depending on which kind of squash you're building. My crooknecks have a bulb while my zucchini have a thicker stem than the males but not a bulb shape. I had never grown squash before this year, and it's been a learning process. "Why are my males so big and the females so small/non existent? When will my female flowers bloom? How do I know if they're pollinated? When do I harvest them? What happens if they don't pollinate?" I found myself tackling all these questions in about two weeks as suddenly my plants started pushing out female flowers and fruit.
To answer your question completely, I've never seen a female flower without a swollen stem behind it that eventually becomes fruit, and if there isn't any, then I don't know what could cause that. :(

Yeah... what makes you think they are female flowers if there isn't a baby squash at the base of the flower? Pictures would be fairly definitive.

I too have seen no females all season! been like 3-4 weeks and all male flowers every few days, until this past weekend when i saw ONE female starting to grow ( hopefully will flower soon). i really hope my zucchini plant doesnt produce only 1 fruit all summer lol

I've got the opposite - all females, haven't seen a male yet. Thinking of asking my neighbors if one of their plants can make a pollen donation ;-)