Mamma Come Home

Humanity is contacted by aliens who are, in appearance, totally like human women, except for one difference: they are about twice the size of a normal human. These "Girls from Capella" are given the royal treatment, and tour all over Earth, while dropping hints that there is some connection between humans and their own species.

In short: it turns out that humans are the same species, but with some mutation or other that prevents the women from growing huge upon maturity, leaving them the same size as men. The 'aliens' are from a female-dominated society which treats men as property, and they--now that they know of such a valuable source of defenseless men--intend to take up the age-old occupation of slave-trading. To ensure that the Earth remains available for their poaching, they plan to block out much of the light from the sun, sending the Earth into an ice age and preventing the sort of technological development that might allow humans to defend themselves.

Ultimately, the humans concoct a forged movie depicting a giant male creature raping a Capellan, accompanied by the dire warning to flee from the homeworld, which has been overrun by these monsters. Without a market, and with such a terrifying threat, the Capellans flee Earth immediately.