Are rats really taking over our cities? | Jonathan Richardson | TEDxRVA Youth

Rats have long been cast as villains, symbols of disease and decay, but viewing them as ecological messengers could be more productive. Two types of rats exist: one contributes to medical research, leading to new treatments, and exhibits pro-social behaviors like helping trapped companions. The other is an urban menace, transmitting over 50 diseases, causing billions in crop damage, and damaging buildings and infrastructure. While one is used to detect landmines, the other has invaded nearly every continent, implicated in the extinction of many bird and mammal species. Despite varied perceptions, understanding rats is crucial. Research into wild rats reveals a surprising lack of knowledge about their real-world behavior and ecology. One study reviewed over 300 papers, finding that rats harbor more than 50 diseases that can infect humans. Cities with less sanitation infrastructure and higher social and income inequality had rats carrying more diseases, suggesting that disease risk is intertwined with human decisions about urban and economic development. Another study mapped where rats thrive in cities, finding clusters in dense neighborhoods with older buildings, less green space, and lower socioeconomic indicators across eight cities. To determine if rats are indeed "taking over" cities, long-term data on rat sightings and inspections from 16 cities was collected. Three-quarters of these cities showed clear increases in rat populations, indicating a rise in most cities globally. Two key factors contributing to this rise are urbanization and climate change. Cities with more people, concrete, and less green space experienced faster growth in rat populations, as more people generate more waste and built environments offer more shelter. The strongest relationship, however, was with temperature. Cities that warmed the most in recent decades saw the sharpest increases in rat populations. This is biologically sound, as warmer winters mean rats spend more time above ground feeding and reproducing, leading to higher winter survival and population booms. These increases in rat populations are not just a nuisance but a signal of profound environmental changes. If rats thrive due to how we build, manage, and heat our cities, then the focus should shift from eradication to understanding what their numbers reveal about weaknesses in our urban systems. Rats flourish where human systems falter, such as aging infrastructure, poorly managed garbage, and high inequality. Tracking rats systematically can provide early warnings about accumulating stresses. Ultimately, basic solutions like reducing food waste and sealing garbage bins are critical. The deeper lesson lies in designing cities where rats don't find opportunities to exploit. This is not just about rats, but about how we coexist in cities with each other and with species that adapt to the worlds we create. By understanding how rats thrive, we can build cleaner, fairer, and more resilient cities for everyone.