Reading primary research literature is an essential skill for scientists. However, the high complexity of research papers may pose a barrier to the development of scientific literacy. In semi-structured interviews, we explore how 33 biologists including undergraduates, postgraduates and researchers approach reading an unfamiliar scientific paper. We find that some readers are data-centric, focusing on their own critical evaluation of the data presented, whereas others adopt a more narrative-centric approach, relying on the descriptions of authors to inform their understanding. There was a bias towards undergraduates adopting the narrative-centric approach and researchers adopting the data-centric approach. All postdoctoral researchers and academics prioritised critical interpretation of the data, indicating this is a characteristic of experienced scientific readers. The ability to demonstrate scientific reading skills was context-dependent, particularly with respect to time available and whether a paper aligns well with a reader's specialist area of knowledge. Inexperienced readers often lacked sufficient prior knowledge on which to base their reading, which represented a barrier to their engagement. We make recommendations for how scientific literacy should be developed within undergraduate teaching and beyond, noting that 'one-off' teaching strategies are insufficient when the development of scientific reading skills is a career-long process.