The first clause may be understood
Like the noise of a flame of fire that devoureth the stubble. This was the noise made by them, not when they were properly in motion, but when alighting on a district they devoured every green thing in plant, or shrub, or tree—the noise, in fact, which they made when feeding. It resembled the crackling of flame ever a field of grain or stubble set on fire. Such was the noise they made when marching, and such the noise they made when foraging—the one was like the rattling of a chariot, the other the crackling of fire. Cyril notices this peculiarity as follows: "They say that their alighting in the fields is effected not without noise; but that a certain shrill noise is produced by their teeth, while they chew into pieces the prostrate grain, as of wind scattering flame." Thus Thomson also says, "The noise made in marching and foraging was like that of a heavy shower on a distant forest." As a strong people set in battle array. Their progress is thus described: "Their steady though swift advance and regular order resembled an army well equipped and in battle array on its line of march." Cyril says of them, "By reason of their innumerable multitude, not easy to be encountered, but rather very dangerous to be met with." Again he says, "They are an irresistible thing, and altogether invincible by men." Here again the prophet's description is confirmed by the observation of intelligent eye-witnesses. Referring to Solomon's statement, "The locusts have no king, yet go they forth all of them by bands," Dr. Thomson says, "Nothing in their habits is more striking than the pertinacity with which they all pursue the same line of march, like a disciplined army. As they have no king, they must be influenced by some common instinct."