This plague comes without any warning, as do the sixth and ninth plagues. Furthermore, this plague is not said to cease. Maybe each triad of plagues has a third, permanent reminder of that triad (Enns, pg. 210). The plague of darkness might cease because there is no triad to follow (Enns, ibid).
It is not certain what kind of bugs these were. Various translations could be given: flies, gnats, lice, mosquitos. But they were irritating, scratchy bugs that left even the magicians unclean (and therefore unable to pursue their offices; see Ryken, pg. 242, quoting John J. Davis). But what may be more important than what they are is where their origin is (Enns, pg. 209). They come from the earth. Possibly this is an attack on the god of the earth Geb, pictured above (Ryken, pg. 240). The earth itself, a power over which the Egyptians did not claim the same kind of power as it did over the Nile, is now turned against the Egyptians, as the water had already. We will also see the air turn against the Egyptians.
Pharaoh had the responsibility to keep ma’at in the world (Ryken, pg. 241). This word means “order.” By decreating Egypt, God, in showing the Egyptians the logical outcome of their idolatry, shows Pharaoh that Pharaoh is not the keeper of ma’at, Yahweh is. The magicians recognize this, at least partially, when they say that “this is the finger of god(s).” It is not certain whether they are affirming their own pantheon, or the God of Israel. At any rate, they acknowledge that they are out of their depth.
We expect certain things like money, pleasure, and power to keep our lives in good order. At the very least, our schedule ought to keep us in order. However, God only keeps the timetables. Jesus Christ has broken the power of all so-called gods in His death and Resurrection. Therefore we should trust in the One who has conquered.