Bats leave dark-colored guano that looks like little pebbles. It is usually found around where they are entering or exiting your house.
Stains and Streaks Around Openings or Spaces on the Exterior of the House
These streaks are usually dark (black or dark brown) oily marks where bats are squeezing themselves into small openings to get into your house or attic.
You Hear Sounds in Your Attic
Bats can be quiet in flight, but when they get into small, tight spaces like attics and behind walls they can make quite a bit of noise. Their flying technique in enclosed areas can cause them to bump into air vents, support beams, and hit drywall when coming in and out of your house.
You See Bats In or Around Your Home
This may come as a surprise to some, but when you see bats flying near your house at sunset or in the evening – they are not going to caves or “haunted houses” someplace far away. They may have become quite established in your attic or inside your walls. The more bats you see and the frequency that you see them are strong indicators as to how bad the infestation may be. (And, if you happen to find a “loose bat” inside of your house… chances are he’s not “lost” and just happened to fly into your house through a window or door. He’s likely got a lot of friends in your attic or walls).
Strong Smell Coming from Your Attic
Bat guano (droppings/poo/urine) can smell very strong, much like an ammonia smell. Many times we will have to use masks or other protective clothing because of the bitter smell and amount of guano droppings that become piled up inside homes and attics.