A common strategy terran players use against zerg is to go after demons early in the game. Hellions are very good against Zerglings and Banelings when they don’t have their speed buffs. The reason is that, with the right microdemons, Banelings and Zerglings can be committed without them even taking a good hit against them.
Sure, later on, when you’ve spread your creep and gotten a metabolic boost for the zerglings, you can go around them, but by then they’ll have done enough damage to your economy to put them in the lead. They can then transition to other units and expand.
In order for you to prevent this from happening, you just need to go to the cockroaches. Cockroaches are so good against demons. Don’t just rely on queens and thorn crawlers because this will make it difficult if you decide to get a baneling nest instead of a roach burrow.
You need to scout your opponent to make sure they go after the demons. They will likely build it away from the ramp so you won’t see it. That’s good for the overlords because they should be able to get there on time. Just build your economy and protect your expansion with a couple of well placed spinal crawlers and have queens protecting too.
If you see a factory or even two with a reactor under construction, that probably means they’ll have daemons. In case they go for siege tanks with marauders, you should also get zerglings with some roaches.
Marauders and Siege Tanks work well against roaches, but not so well against zerglings. Also be sure to quickly upgrade mutalisks to air-kill them. They probably won’t have much flak since they’ll be investing their resources in their tech.
Just make sure to protect yourself with your roaches and then have the mutalisks attack and harass their base. If they wait too long to expand, they will be able to advance the economy. Just keep up with your macro and protect your base. Have vision between you and your opponent, especially if they are in siege tanks because you will want to attack them before they reach your base and go into siege mode.
That’s what many players don’t understand, is that roaches can be useful if they are controlled correctly.
