Should Researchers Use Fruit Flies Instead of Mice in Pain Research?

Abstract The Guide for the Care and Use of Laboratory Animals , the standard reference work on animal research ethics in the USA, interprets the 3Rs as recommending “relative replacement,” where animals should be replaced by others that are “lower on the phylogenetic scale.” This means, for instance, that researchers should use a Drosophila model instead of a mouse model when they can. However, this may conflict with the precautionary principle, which implies that researchers ought to give the benefit of the doubt to animals that might be sentient – which, on the face of it, means that they ought to treat that animal like any other. So, the precautionary principle seems to imply that researchers should not use a Drosophila model instead of a mouse model. This case study explores this seeming tension, identifying the powerful considerations that support both replacing mice with insects and giving insects the benefit of the doubt. Then, it considers some ways forward based on the observation that the tension between the 3Rs and the precautionary principle is not a conflict between competing values. Both the 3Rs and the precautionary principle are motivated by the same value: namely, minimizing unnecessary harm. So, when deciding on how to proceed, researchers should engage in a broader harm/benefit analysis. In addition, they should do their best to employ humane practices whichever species they opt to use. Information © The Author 2025