(CBS) — Chicago is the rattiest city in America, according to pest control company Orkin. The company released a top 20 list with Los Angeles, Washington D.C. and New York City trailing Chicago.

“Each city on this list is a major urban area that provides ideal conditions for rats and mice to thrive,” said entomologist and Orkin Technical Services Director Ron Harrison, Ph.D. in the release.

The list was based solely on the number of treatments performed by Orkin in the past year.

Orkin estimates rats and mice invade 21 million American homes each year and one-third of Americans saw a rodent in their home according to a 2013 study.

Below is the full Orkin list:

1. Chicago
2. Los Angeles
3. Washington, D.C.-Hagerstown
4. New York
5. San Francisco-Oak-San Jose
6. Seattle-Tacoma
7. Detroit
8. Cleveland-Akron-Canton
9. Baltimore
10. Miami-Ft. Lauderdale
11. Dallas-Ft. Worth
12. Denver
13. Houston
14. Atlanta
15. Boston-Manchester
16. Minneapolis-St. Paul
17. Sacramento-Stockton-Modesto
18. Syracuse
19. Indianapolis
20. Charlotte