Wiktionary
drop like flies
vb. (context simile of members of a group, especially soldiers English) Die en masse, one after the other.
Usage examples of "drop like flies".
They skip town, or turn perfidious, or else they drop like flies, and then where are you?
He's done well by her, the restaurant and all and so good with the children, but it mystifies me why they drop like flies for Beth.