When it is too warm to sit outside, I often sit at the dining table on the ground floor of my house by the open window that gives on the terrace. Every now and then an insect comes in to explore the house. Most often these are flies, but wasps and bees are not far behind in numbers. As insects fly hither and thither, I watch them without blinking. Trying to figure out what they are searching for, I follow their every move until they leave the house, which they usually do after a minute or two. As I am following a bee right now, I suddenly realize that I have never seen an insect take the stairs to the first floor. Not once in almost six years.