This paper analyzes public understanding and moral reasoning with regard to regulating nature, specifically, societal efforts to control an insect population. It presents a study of a Swedish case in which a biological insecticide has been used to fight mosquitoes to reduce the nuisance to the local population. This case involves conflicting values regarding environmental protection. People's right to outdoor life is placed in opposition to long-term risks to biodiversity. Through interviews with local residents, their deliberations on the spraying are analyzed, particularly concerning to what extent and how they describe the situation in moral terms, but also how they acknowledge and use scientific findings in their argumentation.