Rats pose. a threat to humans by spreading diseases via food supply. They have a reputation for destroying and contaminating insulation, wood, electrical work, vapor barriers and air ducts. At about 8″ long (its tail adds another 6 inches) and weighing as much as a pound, these nocturnal rodents are able to enter through a hole in a structure as small as half an inch. They tend to nest in lower structures such as burrows, around water sources like rivers and streams and even under sidewalks. Their diet includes grains, meat and fish. Coarse, shaggy hair covers their thick body and can vary in color. Droppings are a sure sign of a rat infestation.