Several factors have been identified that could be responsible for the collapse of honeybee populations. However, Raymann et al. have identified an antibiotic that appears to reduce bee survival by changing the bee microbiome. Hives are frequently treated with tetracycline to prevent infections. When bees were fed tetracycline for 5 days in a laboratory and reintroduced to their hives, half as many survived after 3 days, relative to controls. Antibiotic treatment decreased the number and relative abundance of the bacteria living in the bee gut. After treatment, bees were more sensitive to infection by a Serratia species of bacterial pathogen. Bees that were germ-free showed no changes after tetracycline treatment, suggesting that tetracycline was acting on the microbiome and not directly on the bees.