We've all heard of the old saw about women who let themselves go after getting married. Well, female ticks take this post honeymoon weight-gain to extremes. After mating, female ticks in the family Ixodes increase their mass an astonishing 100 times, ballooning from the size of a sand grain to that of a kidney bean. This post-copulatory growth spurt is actually an important part of the tick's whole blood-sucking lifestyle. Female ticks need to fully engorge before they can lay eggs. But virgins are better off staying small so that they'll have more time to find a mate. Not that male ticks have anything against full-bodied females. It's just that ticks meet their matches while they're hanging around on their hosts. And if unwed females become too unwieldy they're more likely to get knocked off during a good grooming. As to what spurs the females to really bulk up, Ruben Kaufman of the university of Alberta finds that male ticks' semen contains proteins that trigger engorgement.