Think if "flies" is a noun in that formulation you'd put a semi colon or full stop in there and leave it to the reader to ponder if there actually is any connection between the dubious use of the soldier by the student and the ambitious experimentation by the flies...
I think it’s pretty unambiguously a verb in that case. That kind of comma is very commonly used in literary prose and essentially always is an “and” like conjunction that joins multiple actions together.
