[quote=Tyki]
the zerg can take repeated lightning strikes and have in the past. roaches can move undetected up to the point they attack, killing makarov. the zerg are immune to temperature as is proven by some species of feral zerg living in lava while every strain is capable of deep space travel. she still can't get through their carapace (again a case of underestimating how fucking tough something is) gajeel might kill some of them but up against something like hydralisks or even banelings he's boned. and natsu's one trick is fire... which would be canceled by the countless other powers the zerg would have by the time of reaching the city
[/quote]

Allow me to give you a picture of how strong Erza is. She was powerful enough to slice through indestructible airspace, slicing through solid air. Solid air would be harder than multiple layers of armored steel, nearly indestructible. Furthermore, her armor is capable of taking hits powerful enough to shatter cities and stand back up. Then, recently, she got her Essence awoken and became 3x more powerful than before. Like I said, Zerg are crackers.
Gray, I admit, would probably be pretty useless against the Zerg. They seem to be mostly immune to cold. However, he can create massive cannons and blades out of ice with the power to blast houses to pieces, with ease. Furthermore, his speed and strength is incredible, far surpassing human limits. Again, recently got awakened, now 3x more powerful than before.
Gajeel can cut entire islands in half, and his skin is hard enough to take tank shells without a problem. He can crush tanks with his bare hands, and Hydralisk bolts wouldn't even hurt him. His roar of blades tears apart cities with ease. Again, he got his Essence awoken.