I was given the privilege of touring a rooming house room that had been unsuccessfully chemically treated for over a year. The tenant commented that he observed the bugs climbing the walls. The tenant input was initially ignored due to the improbability of that observation but then out of desperation the landlord inspected the light fixture in the ceiling. The steel and glass light fixture was filled with bed bugs.
This relatively unusual behaviour does have some explanation. The exterminator had made the rest of the suite uninhabitable for bed bugs with constant chemical treatments and the bed bugs decided to find alternate harbourages. Though the glass and steel substrates were not preferred substrates the bugs decided that this harbourage was superior to chemically treated areas with better substrates. Every night the bugs would climb down the walls to obtain a blood meal and then return to the light fixture.
Now we know that bed bugs can sense carbon dioxide from about 5 feet and heat can be sensed from about 1 foot. There is also a small attraction for certain smells but has been shown to be relatively insignificant as an attractant. We know that carbon dioxide is heavier than air and accumulates at floor level so these bugs on the ceiling could not have followed the carbon dioxide. The smell is relatively unimportant and heat was too far away to be noticed so how did these bugs find the host? There is some speculation that the bugs follow pheromone trails similar to ant behaviour. If pheromone trails are shown to be one of the cues bed bugs follow it might be unwise to wash the floors. Perhaps floor washing might cause some bugs to wander elsewhere which is not good– it is always good to know where the bug is going when trying to kill them.
Or perhaps they follow visual movement cues? We do not know. There is so much we do not know.