Insects are convenient models for assessing the virulence of microbial pathogens or for assessing the ­efficacy of antimicrobial drugs and give results comparable to those that can be obtained using mammals. Galleria mellonella larvae are easy to purchase and inoculate and provide results within 48 h. Various parameters may be used to monitor the effect of a pathogen on the insect and, as a consequence, measure its relative virulence. Larval death, changes in immune cells (haemocytes) numbers, or the extent of proliferation of the pathogen within the insect haemocoel are good indicators of virulence and of the insect’s immune response. Analysing the humoral immune response also gives insight into the interaction of the pathogen with the insect. Changes in gene expression or the expression of key antimicrobial peptides provide data on this element of the insect’s response and, through extrapolation, how the mammalian immune system might respond. G. mellonella larvae, therefore, provide a quick and convenient means of measuring microbial virulence and are a useful alternative to the use of mammals for this type of screening.