There are 3 main differences between a rat & mice infestation: 1. Droppings - rats tend to have much larger droppings than mice, making them a little easier to identify straight out. 2. Behavior - rats are typically very cautious, which is why you may not know of their presence for a long time, whereas mice are very curious and therefore likely to scope out anything new in your home. 3. Breeding - Mice breed very quickly, so it is easier to have an infestation of these pests than with rats. Rats primarily breed in the spring, making this the prime time to put a stop to an infestation.