Do you know what a mouse model is? The bodies of humans and mice have a lot in common. So scientists often use mice (Mus musculus) as a model organism (or stand-in) to mimic human diseases and discover how the body can stay healthy. Scientists usually keep mice in super clean environments and test them under constant conditions. But most humans don’t live in labs! So how well can a mouse model represent real life? We decided to test how a realistic environment impacts the ability of mice to fight off intestinal worms. We took our laboratory-born mice outdoors to dig in the dirt, search for food, and live like wild mice. But when we gave them intestinal worms, the mice that lived outdoors couldn’t clear the infection as well as indoor mice. In fact, the mice that lived outdoors the longest developed fatter and longer worms in their guts. Our outdoor mouse model shows the effects of the environment on experimental results.