If you thought the sex lives of humans were complicated, consider the case of the female Aedes aegypti mosquito, bringer of Zika, dengue, and yellow fever: She mates but once, in seconds and on the wing, with one lucky male; spurns all further advances from other potential suitors; and stores enough sperm from that single encounter to lay more than 500 eggs, which she nourishes with the blood of human hosts.