Field biology courses can be formative learning experiences that develop students' science identities. Yet, they can also pose challenges to students that may disaffirm their science identities--especially to those who identify with underrepresented, excluded, and minoritized groups. It is largely unknown how students' social (e.g., gender) and personal (e.g., where they grew up) identities intersect with their science identities in field biology courses. Therefore, we used the Expanded Model of Science Identity to determine: (1) the factors that influence students' science, social, and personal identities; and (2) whether and how these identities intersect in field biology courses. Using a card sorting task during semistructured interviews, we found variation in science identities with which students identified, mediated by social factors (e.g., social comparison). These social factors influenced how students' social and personal identities intersected with their science identities. Intersections between students' social and science identities were also facilitated by structural factors (e.g., privilege, lack of representation) that perpetuate inequities in field biology. Based on our findings, we offer suggestions to support welcoming, equitable, and inclusive field biology education that nurtures the science identities of all students.