The answer to 'why is my spider trails' is that spider trails, also known as web trails or silk trails, are a common sign of spider activity in your home. Spiders leave these trails as they move around, using the silk to mark their territory and find their way back to their web or hiding spot.
Some common causes of spider trails include an increase in the spider population, a change in the environment that is driving spiders indoors, or simply the natural movement and exploration of spiders as they search for food and mates. While spider trails are not necessarily a sign of an infestation, they can be an indicator that you have spiders present in your home.