The tiny fruit fly (Drosophila bifurca) holds the record for the longest sperm. Researcher Scott Pitnick of Bowling Green state university, Ohio, found that the fly produces sperm that are 60mm long - about 20 times its own length. In comparison, the human sperms are just 50 thousandth of a millimetre.

To produce these sperm, the fly has large testes wound up like a rope that occupy most of the fly's body. Adds Pitnick, "About half of their adult life, about 2 weeks for males, is spent in a non-reproductive condition. That time is taken up just growing these damn testes."