I've got to admit, I'm confused by something here. I'm watching 2x20, and the two Hives heading towards Earth is treated as a bit of a doomsday scenario. But I'm confused as to exactly how they are such a threat - even assuming that at this juncture, Earth depleted the ZPM powering the Ancient weapons chair.
If the Wraith were to bombard Earth from orbit, they'd be killing all the humans they're trying to feed on. And it's not like they have massive information about Earth society, so how would they know where to target more strategically? It's not like sensors designed to detect Ancient weapons chairs are going to locate Earth-made chemical based weapons stockpiles.
It seems to me like a couple hundred Darts, whilst nasty, would not withstand the planet's military. The United States Air Force (USAF) alone has ten times that many air-to-air fighters according to Wikipedia, and Darts are shown to be quite vulnerable to Earth-made anti-air weapons. Even if the Wraith strategically bombarded all of the airfields before sending out the Darts, there are probably more than enough hand-held anti-air launchers to take them down.
Not to mention that even thousands of Wraith warriors on the Hives is not an awful lot in terms of modern military components, and the Wraith are never shown deploying any kind of land vehicle or heavy land weaponry. You can't exactly stun a tank.
In short, not that Earth forces would not take losses, but I struggle to see how the Wraith could effectively cull a planet the size of Earth with perfectly effective anti-personnel and anti-air weapons. I found the Goa'uld to be a more believable threat because orbital bombardment was a viable option for them- they had way more ships and didn't want the human population to survive.
So how is it that the Hives are treated as such an epic threat?