This paper addresses an explorative case study on Spanish primary pre-service teachers' (PSTs) emotions about, and their interest in, insects. The study is part of a teachers' training programme on insects and the problem of the decline in pollinators conducted at the University of Santiago de Compostela, using scientific practice-based learning approach. The research questions are: (1) "What are PSTs' emotions towards insects and what elements mediate these?" (2) "To what extent are insects interesting for PSTs and what criteria do they use when justifying this interest?" (3) "Is there a statistically significant association between PSTs' emotions towards insects and their interest in them?" To answer these questions, a content analysis was conducted on individual written responses to an open-ended questionnaire along with statistical analysis. Negative emotions are prevalent among pre-service teachers regarding most insect species, and morphology is the factor most strongly correlated with these negative emotions. A significant association was found between the participants' interest in insects and the emotions they displayed, demonstrating that the participants' lack of interest is influenced by their negative emotions. The implications point to the need to design training programmes oriented to help teachers overcome negative emotions and develop an interest in invertebrates.