Your actor class has a position. If you implement it there, you don't need to implement it in your subclasses bug and ant again.
You Actor has a position, but your grid also saves the position. That's redundant. If one changes, the other might stay the same and you get an inconsistent state. You only need one entity in your model to save the position. Either the grid or the actors.
Your grid knows about bugs and ants. If there is a certain logic what happens to bugs or ants, maybe it would be better to put it in it's own class and keep the grid agnostic of the rules of play.
In general, you might want to let us know what you are trying to achieve. In plain normal english. Without code. Because although we might be good coders, we generally suck at telepathy. We don't know what you want. We only see what you tried. And it's hard to suggest better designs without a clue what the goal might be
