Albert Barnes Commentary Jeremiah 51:27

"Set ye up a standard in the land, blow the trumpet among the nations, prepare the nations against her, call together against her the kingdoms of Ararat, Minni, and Ashkenaz: appoint a marshal against her; cause the horses to come up as the rough canker-worm." — Jeremiah 51:27 (ASV)

Ararat, see the (Genesis 8:4) note. Minni is probably the western portion of Armenia, as Ararat was the portion in the center and to the east. Armenia was at this time subject to Media. Ashchenaz was between the Euxine and the Caspian Seas.

A captain — Some prefer the Septuagint rendering in (Nahum 3:17): “a mingled mass of people.” (Others, a “scribe,” an Assyrian term.)

The rough caterpillars — i.e., locusts in their third stage, when their wings are still enveloped in rough horny cases, which stick up on their backs. It is in this stage that they are so destructive.