Biologically inspired design is a rapidly growing movement in environmentally sustainable design. According to the biologically inspired design paradigm, nature is the best design case base. This recognition has led to a race to develop case-based techniques and tools to aid biologically inspired design. It is noteworthy that all current case-based tools perform only the task of generation of design concepts. However, some cognitive studies have suggested that case-based reasoning plays an important role in design solution evaluation and design solution explanation in addition to design concept generation. In this paper, we describe an ethnographic study of biologically inspired design that confirms the above finding. In addition, our study indicates that case-based reasoning may support a fourth task in biologically inspired design especially in the context of collaborative design: explanation of biological source cases. These findings suggest a significantly expanded role for case-based reasoning in biologically inspired design.