Albert Barnes Commentary Habakkuk 1:8

"Their horses also are swifter than leopards, and are more fierce than the evening wolves; and their horsemen press proudly on: yea, their horsemen come from far; they fly as an eagle that hasteth to devour." — Habakkuk 1:8 (ASV)

Their horses are swifter - literally, lighter, as we say "light of foot."

Than leopards - The wild beast intended is the panther: the lightest, swiftest, fiercest, most bloodthirsty of beasts of prey. "It runs most swiftly and rushes brave and straight. You would say, when you saw it, that it is carried through the air." Cyril states: "It bounds exceedingly and is exceedingly light to spring down on whatever it pursues."

More fierce -

Than the evening wolves - , that is, than they are when fiercest, going out to prey when urged to ferocity by hunger throughout the whole day. Their own judges had been such (Zephaniah 3:3), and by such they would be punished. The horse partakes of its rider's fierceness in trampling down the foe.

Their horsemen will spread out - literally, widespread are their horsemen.

And their horsemen from far will come - Neither the distance of the march will weary them, nor diffusion weaken them. Thus Moses’ prophecy would again be fulfilled (Deuteronomy 28:49–50, where מרחוק occurs in both): The Lord shall raise against thee a nation from far, from the ends of the earth, as the eagle flieth; a nation whose tongue thou shalt not understand; a nation of fierce countenance, which shall not regard the person of the old, nor show favor to the young.

They will fly as the eagle that hastens - literally, hasting.

To eat - Jerome comments: "not to fight, for none will withstand; but with a course like the eagle’s, to whom all fowl are subdued, hasting but to eat."

Indeed, Jeremiah says of Nebuchadnezzar (Jeremiah 48:40), he shall fly as an eagle and spread his wings over Moab; and he repeats the words (Jeremiah 49:22) over Bozrah. Jeremiah also says (Lamentations 4:19), Our pursuers are swifter than the eagles of the heavens. Ezekiel likens him to (Ezekiel 17:3), a great eagle with great wings full of feathers; and in Daniel’s vision he is (Daniel 7:4), a lion with eagle’s wings.