What the gluey heck?

When I got back to Lexington on Wednesday, I noticed a line of sticky something running straight along the sill below the storm door on the front porch. That explained the sticky spots on the floor - they had been tracked in while I was away. Arthur doesn't walk barefooted around the house, so it escaped his notice. This morning I finally decided to clean off the sill, but it was dry and not sticky at all. I asked Arthur if he had cleaned it. Nope. Next was a line of almost clear very sticky goo along the doorway to the basement. After all these years, is sap coming out of wood in the house somehow? Poltergeists leaving a warning? We have large black ants in the kitchen and downstairs bathroom, seemingly looking for water (I have found more than one in the toilet bowl, for example). Do ants exude something along doorways?