In the 1967 Star Trek episode “The Trouble with Tribbles” Dr McCoy discovers “Well, the nearest thing I can figure out is that they’re born pregnant—which seems to be quite a time-saver.”
I always thought this was one of the funniest lines in the episode. It couldn’t really happen, though, could it?
This is a mite of the genus Adactylidium. It’s a lot smaller, and less furry and lovable than a tribble, but it’s essentially born pregnant. The mite is a parasite which feeds on the eggs of tiny insects called thrips. The female eats the egg and develops five to eight female offspring and one male in her body. The male impregnates the unborn females, who then eat their way out of the mother’s body. They then seek new eggs upon which to feed. The male neither feeds nor seeks new mates and dies after a few hours. The females who are successful in finding a thrips egg live for about four days, when they are eaten alive by their own offspring.
Which seems to be quite a time-saver.