Learn which rapidly breeding animal can have more than one million descendants over 18 months.
Did you hear the one about how rats multiply so quickly that in 18 months, two rats could have more than a million descendants?
It's mind-blowing to think about, but is it true?
Rats do have a remarkably high birthrate. According to the University of Michigan Museum of Zoology, an average female rat can give birth about seven times per year, to a litter of about eight pups each time.
All told, the birth rate can reach about 60 young per female each year. And since it only takes a female rat about four months to reach sexual maturity, many of those 60 new rats could be birthing broods of their own pretty quickly.
Here's something else to ponder: A female rat goes into heat for about six hours at a stretch. During this rather brief window of time, she can expect to mate up to 500 times.