New research suggests that brown rats crawled off ships earlier than previously thought and quickly out-competed rival black rats to take over North American cities. The study, published Wednesday in the journal Science Advances, suggests the species first appeared on the continent before 1740. Brown rats were bigger and more aggressive, and scientists say they may have eaten food that black rats otherwise would have. Today, brown rats are so ubiquitous in North American cities that they’re known as common rats or street rats. Experts say knowing which rats lead the pack can help cities better manage their populations.
