The answer to 'why is my wasp trails' is that you are likely seeing the pheromone trails left by worker wasps as they travel between their nest and sources of food or water. Wasps use these chemical trails to mark pathways and guide other members of the colony to resources.
Wasp trails are a common sign of an active wasp nest nearby, usually located in a sheltered spot like under eaves, in a tree hollow, or in the ground. The trails can appear as a series of thin, dotted lines leading away from the nest entrance. Seeing these trails is an indication that you have an active wasp problem that may require professional pest control treatment.