New Study Finds NYC Mice Developing Poison Resistance, Rats Learning to Escape Traps

A recent study by researchers at Rutgers University has shown that house mice in the New York City area are developing genetic resistance to common rodenticides, while nearby brown rats are improving their ability to avoid physical traps.

The study, published in the journal Pest Management Science in June 2026, examined DNA samples from 300 rodents collected in urban environments across New Jersey, Pennsylvania, Washington, D.C., and New York City. The samples included house mice (Mus musculus) and Norway rats (Rattus norvegicus). Researchers focused on a gene called VKORC1, which is known to influence sensitivity to anticoagulant rodenticides.

They found that about 70 % of the house mice carried a mutation in VKORC1 that reduces the effectiveness of these poisons. The mutation allows the mice to survive exposure to the chemicals that are widely used in residential and commercial pest control. According to postdoctoral fellow Jin‑Jia Yu, who led the genetic analysis, “When the mice eat the poison, they can still function normally, basically. That’s why they are more tolerant.”

In contrast, the brown rats did not show the same level of genetic change. Instead, researchers observed behavioral adaptations. Video recordings of rats in the Bronx revealed that the animals could avoid snap traps and sticky traps that are commonly deployed by pest‑control professionals. The rats would approach a trap, learn from the experience, and then avoid similar devices in the future. Changlu Wang, an extension specialist who co‑authored the study, noted that “We have a lot of video clips showing that the rats can avoid the physical traps. They can spend one week or 300 approaches before they even touch the traps.”

The findings raise concerns for city officials and pest‑control companies that rely heavily on chemical and mechanical methods to manage rodent populations. Continuous use of anticoagulant rodenticides could lead to more widespread resistance, making these products less effective over time. Moreover, the study highlights a secondary risk: rodents that survive poison exposure can become a source of secondary poisoning for predators such as birds, coyotes, and other wildlife that feed on them.

The researchers recommend that urban authorities consider non‑chemical strategies that focus on prevention and sanitation. Measures such as securing food sources, sealing entry points, and improving waste management could reduce the need for poisons and traps. The study also suggests that monitoring rodent populations for genetic changes could help inform adaptive pest‑control strategies.

While the study provides clear evidence of evolving resistance in mice and behavioral adaptation in rats, it also underscores the need for ongoing research. The authors call for further investigation into how these changes affect disease transmission and ecosystem dynamics in densely populated cities.

The Rutgers team’s work adds to a growing body of evidence that urban wildlife is rapidly adapting to human interventions. As cities continue to grapple with rodent infestations, the findings point to the importance of integrated pest management approaches that combine chemical, mechanical, and environmental controls.

The study was funded by the U.S. Department of Agriculture and the National Institutes of Health. It represents the first large‑scale genetic survey of rodents in the northeastern United States that links specific mutations to resistance in real‑world urban settings.