For many, declining biodiversity represents an emotionally and psychologically distant ‘cost’ – similar to how a number of people perceive climate change. Using an expectancy-value theory framework, we showed participants photographs that visibly illustrated the threat of biodiversity loss. Specifically, we tested a combination of preregistered and exploratory hypotheses through an online experiment (n = 843) to understand whether viewing photographs of plants and animals (with and without captions) bolstered people’s valuing of biodiversity and willingness to donate to a nature-focused charity relative to a control group. Participants who viewed photographs (without captions) valued biodiversity more and donated more to the nature-focused charity; those who viewed photographs with captions showed similar though more muted (non-statistically significant) effects. Follow-up mediation analyses on the photographs-only participants suggested that the photographs may have catalysed negative emotions that increased valuing of biodiversity and, in turn, increased donations. This study provides preregistered evidence that thoughtfully selected photographs boost people’s valuing of biodiversity and exploratory evidence that the pathway through which that might occur is more likely via negative emotions than through reduced psychological distance. Educators, conservationists, journalists and others may find these results informative as they develop strategies for addressing the acute problem of biodiversity loss.