In North American forests, odorous house ants (Tapinoma sessile ) lead quiet lives. The insects—called "odorous" because they smell like a piña colada when crushed—make their homes in hollow acorns and form simple colonies of 50 to 100 workers beneath the sway of a single queen. But as soon as they move on up to cities and suburbs, these mild-mannered ants live large, exploding into complex supercolonies of more than 5 million workers and thousands of queens. The insects also begin to act like an invasive species, robbing other ant species of resources and raiding buildings for food, researchers will report in an upcoming issue of Biological Invasions. Future studies will focus on the odorous ant's genetics, in hopes of learning why urban life turns it into such a swarming bully—and how to stop it.