High levels of student anxiety are negatively related to degree persistence, academic achievement, and student perceptions of instructor support. Anxiety levels vary along many axes--among classes, within students in the same class, and over time--creating a dynamic emotional landscape in classrooms. In this study, we examined the relationship between student anxiety levels and perceptions of instructor support within three introductory biology classes at two timepoints during a semester. Data on student anxiety levels and perceptions of instructor support were supplemented by open-ended student explanations of instructor support characteristics. We found a significant negative correlation between student anxiety level and instructor support ratings at wk 4 for all three classes. By wk 14, this correlation persisted in classes 1 and 3 but not class 2, where support ratings no longer significantly varied with anxiety levels. Analyses of open responses revealed that lower-anxiety students in classes 1 and 3 were more positive about how the instructors answered questions and higher-anxiety students in class 2 were more positive about their instructor's pedagogical practices. We suggest that these instructor practices should be investigated as potential factors to equalize perceptions of instructor support by students with different anxiety levels in introductory biology.