Put the pizza away and make sure to vacuum if you live in one of these cities.

Pest-control company Orkin released its annual ranking of cities with the biggest rat problems on Monday. Chicago took the top spot on the list, which includes 50 cities.

Portland was ranked No. 20.

Many of the top offenders were cities in the Midwest, according to the rankings, which are are based on the rodent treatments in each city between October 2015 and September 2016.

According to the pest control company, fall marks the beginning of rodent season.

“Just like we put on a warm coat and turn up the heat indoors, rodents look for a warm place to nest,” John Kane, an entomologist and Technical Director of Orkin’s Midwest Region, said in a statement.

According to Kane, rats can fit into a hole the size of a quarter and mice can squeeze through a hole the size of a dime.

Here's a look at 25 "rattiest" cities in the U.S. according to Orkin:

1. Chicago
2. New York
3. Washington D.C.
4. Los Angeles
5. San Francisco-Oakland-San Jose
6. Baltimore
7. Philadelphia
8. Minneapolis-St. Paul
9. Detroit
10. Denver
11. Seattle-Tacoma
12. Boston
13. Miami-Ft. Lauderdale
14. Dallas-Ft. Worth
15. Cleveland
16. Atlanta
17. Hartford & New Haven, Conn.
18. Pittsburgh
19. Indianapolis
20. Portland, Ore.
21. Houston
22. Raleigh-Durham, N.C.
23. Milwaukee
24. Norfolk-Portsmouth-Newport News, Va.
25. Richmond-Petersburg, Va.

To keep any unwanted rodent guests out, Kane suggests people do the following:

  • Be on the lookout for rodent droppings in your home and outside. Early detection is key.
  • Look for cracks or holes that a rodent might be able to squeeze through. Seal them properly.
  • Clean up any waste that might attract rodents and store food in rodent-proof containers.
  • Install weather strips around doors and entryways to block rodents from getting inside.

Good luck!

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