Grid bugs are one of the weakest monsters. They are nothing to worry about once you pass level 2. They usually deal no damage at all, unless they manage to zap you as well ("You get zapped!"), and even then the damage is very small, thus the only real damage is when they have you cornered (for example in a corridor) next to a more powerful monster. They never leave corpses. Grid bugs are unique in that they cannot move or attack diagonally. Their electric attack does not break your rings and wands unless they are higher level than zero.