lol? zerg makes a spire every game vs protoss for corruptors and the THREAT of a muta switch. The only way of knowing is literally seeing no other gas units AT ALL and a single evo and that's only a tell early game. You CANNOT KNOW when it is coming late game, it is just a continuous possibility that you could lose at any time. gtfo
Lemme know when you're done crying.
Until then, I'll keep talkin starcraft. A muta switch pre-max supply will come when he's making no gas units at all really, and you can capitalize on this by just attacking.
After maxing out, zerg needs a LOT of gas to make the muta switch work. You should know about when zerg is maxed out. Again, this comes down to scouting. If you can't tell this, you're just bad, so rage more. But your late game comp should sh!t on mutas. Late game toss is colossi, void ray, archon, zealot. And a couple high templar. Void rays are really beefy, so they last awhile while archons wreck them, being beefy themselves.
Keep in mind, zerg stockpiling all that gas after maxing, you should have your own bank rolling yourself. That is, unless you're bad. And judging by your approach to this situation, this is the case. Throw down a bunch of cannons and stop b!tching already. You're my favorite kind of person to stomp on ladder.