From Longman Dictionary of Contemporary Englishbe dropping like fliesbe dropping like fliesinformal if people are dropping like flies, they are getting ill or dying in large numbers → drop
Examples from the Corpus
be dropping like flies• Players from both teams are dropping like flies.• Our kids are dropping like flies.• They should be dropping like flies, but that hasn't been the case.• Grocer profits While other retailers are dropping like flies, supermarkets are making fat profits. 