[quote=thewizardguy]
Erza can cut through solid air, Airspace, with her katanas when she wishes. Her slices are sometimes said to be even more powerful than Natsu himself. She'd easily get through them.Gray doesn't need to get through the carapace. His main ability is to freeze things. He'd turn them all too ice. At a certain temperature, biological life simply cannot exist, and he'll freeze them down to that temperature.Gajeel can cut entire islands in half when he wants to. Like Erza, he can often match Natsu, using his Secret Dragon Slayer Technique. The zerg are like crackers before these guys. There are multiple scenes where they tear through entire mountains.Makarov takes ten seconds total to charge up Fairy Law. Ten seconds. Even the greatest Zerg Rush can't beat that.Natsu's most powerful attack was able to push Gilarts backwards three feet. This dude is unstopable. He'd wipe out the average zerg army with a single strike.Oh, and I forgot Laxus, who's even more powerful than Natsu is. He can move at lightning speed, and burn through Zerg with ease, frying their little brains out.
[/quote]

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