I have to agree with Duke Umarth Morte, if 'nids get gunned down while moving across the board, you may not have enough bugs. Even if all your opponents' models are entrenched and ready to open-up fire, only so many models will hit, and only some of that percentage may wound. So at most, you would suffer a moderate amount of casualties, but still have the remainder of your force left.
However this may not work all the time, and it is a bit unfair to have 'nids right out in the open. I think this argument can go either way. Just my two cents.
-Commander Grievous