The Evidence.

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Rodents' teeth are constantly growing requiring them to file them down. Evidence that you have rodents in the attic will start to appear under your roof returns (eaves, see picture). The rubs start small but grow in time and begin to have a smokey, black discoloration. Norway rats produce Sebum often called "Rat Grease". 

Norway rats produce Sebum often called "Rat Grease". Sebum builds up in high traffic areas such as the eaves, pipes and plumbing in the attic, wire stapled to the joists, and entry points around the home. It can look black and smokey or have a brown, greasy discoloration as seem in the picture above.

It can be difficult in early stages of wildlife to notice evidence in the attic. Insulation is a great tool to use to gauge infestation time, size, and duration. In newer infestations, surface trailing on top of the insulation can be faint and hard to see. In longer infestations, deep and matted down trails can easily be distinguished like the photo above.

Droppings are the tell-tale sign to call the exterminator. Every wildlife nuisance produces different dropping types and smells in the attic space. Droppings are typically located on decking, ac units, and throughout the attic space. Most Norway rat droppings will appear egg or banana shaped and appear dark black or brown. Raccoons defecate typically in a singular area in the attic near their bedding. Their droppings are often cat/dog sized and contain berries and other forage. Opossums defecate while moving so it can typically be spread throughout the attic. Fresh opossum droppings appear wet and smooth like black pastel paint.

Sebum will build up in high traffic areas. In older homes, look at the wires where it's stapled to the attic joists, plumbing, ac drip line, and other structures that you may find other evidence such as droppings or disturbed insulation. On the exterior, look for Sebum in the eaves, openings in the home such as soffit holes and weepholes. 

Looking for footprints in the attic can also help you distinguish the type of critter in your attic. Any areas in the attic that collect dust such as ducts, ac unit, stored items such as totes, and trash bags are great areas to look for footprints.