Joel 2:4 - Matthew Poole's English Annotations on the Holy Bible

The appearance of them is as the appearance of horses; their carriage, for fierceness, agility, and irresistibleness, is like that of horses trained up to the wars, of which Job 39:19, &c. And as horsemen, so shall they run: this gives light to the former expression, and by it we see these locusts are not resembled to the horse for shape, but for their nimbleness in motion. And as were these types, so should the armies which were typified be also.