drop like flies, to

To collapse rapidly, referring to a group rather than an individual. Although this term calls to mind flies that are hit with a spray of insecticide and is, in fact, used for human beings subjected to gunfire or an epi- demic of disease, like flies has meant in large numbers or quantities since Shakespeare’s time. “The common people swarm like summer flies” wrote the bard (HenryVI, Part 2 6.8).