🌅 Rat Populations Are Skyrocketing

SOURCE

Richardson et al. (2025)

WHAT TO KNOW

• Researchers at the University of Richmond analyzed public rat complaints and inspection records in 16 major cities around the globe, finding rat populations have “significantly increased” in 11 of the cities (69%) over the past decade or so (the data used in the study was collected over an average of 12.2 years in each city). Washington D.C., San Francisco, Toronto, New York City, and Amsterdam showed the strongest positive trends in rat populations, though the magnitude varied widely across cities; for example, Washington, D.C.’s trend in rat numbers was 3 times greater than Boston’s and 1.5 times greater than New York City’s.

WHY IT MATTERS

• Rats cause an estimated $27 billion in damage each year to U.S. infrastructure, agricultural yields, and food supplies. The murids also harbor and transmit more than 50 pathogens and parasites that infect humans, causing diseases like leptospirosis, murine typhus, and bubonic plague. Overall, cities around the globe collectively spend $500 million each year fighting their respective “wars on rats.”

CONNECT THE DOTS

• The researchers found the growing rat populations were strongly linked to three distinct aspects of urban environments: human population density, urbanization, and warming temperatures. Other data suggests the share of the human population living in cities is expected to increase 25% by 2050, while total urban land cover is projected to nearly triple between 2000 and 2030. As temperatures continue to rise globally, the researchers believe cities could become “increasingly conducive environments for rats” in the coming years.