It is observed by Hebrew commentators that the nine plagues are divided into three groups: distinct warnings are given of the first two plagues in each group; the third in each is inflicted without any previous notice; namely, the third, lice, the sixth, boils, the ninth, darkness.
The dust of the land - The two preceding plagues fell upon the Nile. This fell on the earth, which was worshipped in Egypt as the father of the gods. An special sacredness was attached to the black fertile soil of the basin of the Nile, called Chemi, from which the ancient name of Egypt is supposed to be derived.
Lice - The Hebrew word occurs only in connection with this plague. These insects are generally identified with mosquitos, a plague nowhere greater than in Egypt. They are most troublesome toward October, i. e. soon after the plague of frogs, and are dreaded not only for the pain and annoyance which they cause, but also because they are said to penetrate into the body through the nostrils and ears.