The mark–recapture technique paired with the Lincoln–Peterson index is a commonly used method of estimating the size of animal populations in ecological research. However, this technique is difficult to emulate in an educational setting due to the logistical constraints inherent to the process of capturing and marking live animals. As a result, most lessons on mark–recapture use captive animals or inanimate objects as the focal population. This approach may give students an inaccurate understanding of the potential applications and limitations of the mark–recapture technique. Here, we describe an authentic application of the mark–recapture technique that allows students to gain hands-on experience with the method on naturally occurring ant colonies, a ubiquitous animal system. By participating in this lesson, students will directly engage with the mark–recapture technique to estimate the number of individuals within ant colonies and will learn about the natural history of ants in the process.