A cross section of the thorax of a worker, showing the main thoracic trachea of each side. Trachea from healthy workers should be white with a silvery reflection. The ones here are infected with tracheal mites (Acarapis woodi) and has become brownish or black due to the scar tissue from mite feeding and the presece of many mites. Photo by Prof. M.V. Smith, University of Guelph.