In what's got to be one of the funniest ironies of nature, the world's biggest sperm belongs to a teeny, tiny fruit fly named Drosophila bifurca.
That's 1,000 times longer than an average human sperm.
"To put that into perspective, if humans made sperm that long and you took a six-foot man and stood him on the goal line of a football field, his sperm would stretch out to the 40-yard line," said Adam Bjork, a Ph.D. student at Syracuse University in New York.
Why? Turns out that it's the female fly's fault:
Even after a male has successfully inseminated a female, there's still a long way to go before fertilization can take place. That's because the female bodies of many species are not passive arenas within which sperm compete, but more like obstacle courses, with hurdles and defenses in place to weed out weakling sperm.
In D. bifurca, the female reproductive tract is just slightly longer than the sperm that swim through it.
"It looks like a giant slinky filling her abdomen," Bjork told LiveScience.
The researchers think that it is this exceptionally long reproductive tract that drives the evolution of the giant sperm.