This mission pits you and a group of snipers against a massive influx of spiders. This is made more difficult by the fact that the battle takes place in the middle of a ruined city, and the rubble makes it incredibly difficult to get a shot on the encroaching horde before it reaches you. The answer to this is surprisingly simple. Grab a close combat weapon like a shotgun or assault rifle for any close up work, and an MLRA.

Since the rubble blocks most of your shots, simply aim upwards with the MLRA and sweep from side to side to lock on to different spiders. This will create an aerial bombardment against the spiders. They can do nothing to defend themselves against this technique. It won't net you many power ups, since most of your attackers will die in the distance, but it will make dispatching your foes much easier.