Matthew Poole and continuators on Revelation 9:19

19 For their power is in their mouth, and in their tails , for their tails were like unto serpents, and had heads; and with them they do hurt .

By their Tails some understand their Infantry or Foot-Soldiery; others their Serpentine craft and subtilty; as the Locusts v. 10. are compared to Scorpions, whose Sting was in their tails, and who were said to hurt with their tails; so the same thing is said of these Armies, intimating that the Turks should be mischievous by the same arts and means as their Predecessors the Saracens.

These are said to have had Heads in their Tails, which was not said of the Locusts; the reason of which Interpreters judg to have arisen from the different Animals by which they are represented.