The fly that's been consumed by the fungus is likely Rhagio mystaceus.
On Watercress.
For the fly, see
https://www.inaturalist.org/observations/161166464
Time lapse of newly emerged monarch caterpillar feeding while oleander aphid molts: https://giphy.com/gifs/milkweed-common-aphid-oF5DRBahltEAe7SFn8