From one of several quick eyewitness accounts of locust-swarms:
No voracity is like theirs, the voracity of little creatures, whose million separate appetites nothing is too minute to escape. They devour first grass and leaves, fruit and foliage, everything that is green and juicy. Then they attack the young branches of trees, and then the hard bark of the trunks.' "After eating up the corn, they fell upon the vines, the pulse, the willows, and even the hemp, notwithstanding its great bitterness." "The bark of figs, pomegranates and oranges, bitter, hard and corrosive, escaped not their voracity." "They are particularly injurious to the palm-trees; these they strip of every leaf and green particle, the trees remaining like skeletons with bare branches." "For eighty or ninety miles they devoured every green herb and every blade of grass."Also worth noting is this article about last summer's locust-plague in Afghanistan (the article doesn't mention this, but from teevee tonight, I understand that this particular swarm affected most of Northern Africa and the middle-east last year.)
Finally, a professor at the University of Bath suspects that he may have determined the pheremone responsible for causing swarm behavior in locusts.