Here Yahweh, via Jeremiah, warns them that the destroyer is coming from the north, much like in chapter 4 of this work. The horses and the stallions are snorting and neighing in the territory of Dan, the most northern part of Israel, near Syria. The land was beginning to quake as they are getting closer. They would come and devour the land with everything in it. They would devour their cities and everyone living there. Yahweh was going to let the snakes and the adders loose in Judah so that they would bite them.
David then went into a diatribe description of the wicked ones. He maintained that the wicked peopple were so from their time in the womb, from their birth. This was the nature of the wicked, since there was no question of nurture. They were snakes with their deadly venom whether it be a serpent or an adder group of snakes. This adder venomous snake seems to be smarter or more cunning since it covers its ears so that the snake charmer cannot influence it. This is odd, but not out of line with the thinking that the snake, the adder, or serpent was evil.