Question: What is in my rats fur?

By | August 10, 2018
https://m.imgur.com/mwttbhz?r Is it mites? How do I treat it? Both of my youngest rats have a bunch in their fur, my oldest rat which lives in a separate cage across the room has none in her fur so I’m not sure if it’s because they’re closed to a window or not but I’d also like to prevent it from happening again. Thanks!!