There's no genetic advantage to "finding a way out"! The home barrier way in is a genetic hurdle - flies that cross it are free to reproduce in an abundant env

There's no genetic advantage to "finding a way out"! The home barrier way in is a genetic hurdle - flies that cross it are free to reproduce in an abundant environment. This calls for a "quieter" fly (a stealth fly?) who annoys the local beasts minimally - yet another genetic hurdle.