The age to which the workers live varies according to the amount of labour they undergo. During the winter and the early spring, when little or no work is done, there is small drain on their vital force, and they may live for six or seven months. In the height of summer, when long days and abundant supplies invite them to many hours of continuous toil, the industrious insects are believed to exhaust themselves very rapidly, and to perish, as if prematurely old, in about five or six weeks. It is quite evident that the mortality during the middle of the year must be very great, seeing that egg-laying and hatching go on at the rate of several hundreds a day, and during weeks and months in succession: and yet it frequently happens, where room sufficient for the growing stores is provided, no swarm will be thrown off, from which we infer that a period is reached when the birth-rate and death-rate pretty closely approach each other. The older workers are distinguishable from the younger by their deeper and more glossy colour. The grey bloom of youth has been worn off, and frequently their wings, notched or broken in places, betray the veterans in the battle of life, who, amidst rains, hail, and wind, have suffered more or less severely. Some observers have called attention to certain individuals in the community, which have been spoken of as "black bees,"[1] and which have been supposed to possess special functions. Von Berlepsch ascertained from his countryman Leuckart that no anatomical differences existed between these and ordinary workers; and, from subsequent experiments, came to the conclusion that the difference in colour was due to the accidental absence or the loss of the hairs or down with which bees are ordinarily covered. This loss may have occurred through getting smeared with honey, or from stifling, or fright, or creeping constantly through apertures too small to admit their bodies readily. Dzierzon, another great authority, corroborates the above explanation, and further adds, "as a rule, the glossy black bees are _robbers_, which have been pursuing their trade for some time." [Footnote 1: This term is also used for all English bees, in distinction from the _Ligurian_, _Cyprian_, and other varieties with yellow bands.] A similar difference in size and colour has been often noticed in the case of drones; and the explanation of their occurrence seems to be that such smaller individuals have been hatched in the cells intermediate between the normal drone and worker varieties, a tier or two of such intermediate cells being frequently made, to shade off the difference of size between the two kinds.