Why does the verse compare them to chariots?
Malbim: When horses are joined to each in a chariot, they make noise also with the wheels. Via [the locusts] joining together, they will make noise like chariots.
What is the significance of "Al Roshei he'Harim Yerakedun"?
Radak, Malbim: This is an advantage of the locusts over chariots - they go on mountain tops, but chariots do not. Yerakedun - locusts jump from place to place, like it says "Lenater Bahem Al ha'Aretz" (Vayikra 11:21).
What is the meaning of "k'Kol Lahav Esh Ochlah Kash"?
Rashi: When a flame consumes straw, it makes a noise. Radak - the same applies to thin wood that burns. It says "v'Kol ha'Sirim Tachas ha'Sir" (Koheles 7:6).
What is the comparison to "Am Atzum Eroch Milchamah"?
Radak: Like an awesome nation arranged to fight its opponent. It makes noise and sounds the Shofar to befuddle its opponent.
Malbim: This describes how the locusts will descend from the mountains to the cities - like one who prepares for war against people who try to impede him.
Why does "Eroch" have a Segol?
Rashi: It is because it is Samuch [to Milchamah].
