The rise of the rats

Scurrying in the shadows and lurking under the streets, you can be sure that in any place where there are humans, there are almost certainly rats.

Known for their fierce survival instincts, brown rats prefer to build their burrows in urban sewers and the dwellings of humans, eating one-fifth of foodstuffs planted every year, but contaminating far more.

In major cities like London and New York, some experts say they are as many rats as there are humans, while more conservative estimates put the ratio closer to one rat for every four humans.

To fully understand how the rise of the rats has happened, you must understand the staggering rate that they reproduce.

Swipe the images below to see how quickly two rats can breed in an ideal environment.
0 month 2
2 months 10
6 months 50
9 months 250
12 months 1,248
15 months 6,232
18 months 31,120
21 months 155,400
24 months 776,000
27 months 3,875,008
30 months 19,350,112
33 months 96,626,080
36 months 482,508,800
Month 0 Month 3 Month 6 Month 9 Month 12 Month 15 Month 18 Month 21 Month 24 Month 27 Month 30 Month 33 Month 36

Rat reproduction facts

Why don’t rats outnumber humans?

The speed that rats breed is frightening, but there are many factors that help to stop a population from spiralling out of control.

In a real world scenario, the death rate usually increases as the size of the population grows. Whenever food or space is limited, mortality is high, which partially keeps the rate of population growth in check.

Lack of food and shelter



Pest control



The rise of the rats in numbers

Rat call-outs: 2015 vs 2016

Rentokil saw an increase in rat-related enquiries from 2015 to 2016. In both years, there was a spike of rat call-outs around May.

Which industries are most affected by rats?

Based on over 100 enquiries made to Rentokil.



Auerbach, J. (2014). Does New York City Really Have as Many Rats as People?. Significance, Volume 11 (4), p. 22–27. Available at:

Chace, Z. and Dzotsi, E. (2016). Becoming A Badger. This American Life. Available at:

Long, J.L. (2003). Introduced Mammals of the World: Their History, Distribution and Influence.