drop like flies
Rapidly collapse, die, or drop out, usually referring to a group rather than an individual. For example, The words were so difficult that the spelling bee contestants were dropping like flies. The simile like flies has meant "in large numbers," as it does in this expression, since about 1600.
|drop like flies|
|rapidly collapse, die, or drop out in large numbers; "the contestants dropped like flies when the thermometer hit one hundred degrees"|