When Pound compares modern people to pesky insects and calls them "shells" of real human beings, it might seem like he's being really harsh. And he is. But on the other hand, these images are also some of the easiest to understand in all of Canto VII. This imagery first makes it appearance in line 70, where Pound starts to speak of "Thin husks I had known as men." In other words, he claims that he has seen good people ruined by the modern world and turned into shadows or shells of their former selves.
As the poem continues, Pound accuses these modern people not only of being shells, but also of turning other people into shells by "speaking a shell of speech" and infecting other people with their bitter, empty words.
When it all comes down to it, Pound is suggesting that modern people lack a spiritual core or center that people in the past used to get from their belief in beauty and art. Once these people become shells, Pound more or less loses all respect for them and calls them locusts, comparing them to insects that should be exterminated. The guy isn't all that willing to compromise on his social and artistic ideals, and you really get a sense of it through the anger he expresses in his locust and shell imagery.
Lines 70-72: Pound introduces his shell and locust imagery beyond the midway point of Canto VII, but you can make a strong argument that this is the central, most memorable imagery of the entire poem. When Pound mentions the "Thin husks [he] had known as men," the entire tone of the poem changes. Pound goes from being sad to being angry. Or to put it another way, the first half of Canto VII has a conflict (the absence of beauty), but no real antagonist or enemy to pin the conflict on. From the moment he starts to talk about the modern men as "Dry casques [shells] of departed locusts/ speaking a shell of speech," he identifies his enemies and launches an assault against them.
Lines 74-75: Pound combines his imagery of locusts and shells by specifically comparing the old, modern men to the shells left behind by locusts that have molted. He's accusing these men of having no true, spiritual core, and claims that these men are "moved by no inner being." In other words, Pound doesn't see these people as fully human, though we're not totally sure why. It seems to have something to do with these men not caring about things that matter to Pound, like beauty and personal depth. Instead, these men are just a bunch of phonies whose lives don't matter, and all they add to the world is "a dryness calling for death."
Line 91: Line 91 simply says, "Only the husk of talk," which doesn't seem to add much to Pound's earlier claims about the old men of the modern world speaking with empty, meaningless words. But the fact that this line follows that claim, "The young men, never!" in line 90 shows us that Pound blames the problems of modern society specifically on old people who aren't open to hearing the opinions of the younger generation.
Lines 104-105: Every time Pound seems to gather hope for the future, the image of old, locust-husk men keeps appearing in front of him and discouraging him. After all, the empty speech spoken by these men is hard for just one guy to overcome, even if that guy is Ezra Pound. When it all comes down to it, Pound looks to the future and finds that "the husks, before me, move,/ The words rattle: shells given out by shells." There's only so much he can do as an individual when the entire culture around him has embraced falsehood and emptiness. What's a guy to do?
Lines 106-107: Despite all of his despair, Pound never quite gives up on the project of bringing beauty and depth back to modern experience. At this later point in the poem, Pound thinks of himself as a "live man" in contrast to the dead men around him. He thinks of himself as a man fresh from wandering "out of lands and prisons" and who tries to "shake the dry pods" of modern people, hoping to jar them out of their dry, boring habits and to make something better out of them. In a sense, this image captures what Pound is trying to do with The Cantos in general. He's trying to educate people in the ways of beauty and to get them to live a more authentic life. In short, he wants us to stop being shells.
Line 117: So far in Canto VII, the image of a shell has drawn a clear line between real, genuine people like Pound and the phony, boring old men he's fighting against. But in line 117, we hear mentions of "a more living shell," which totally changes Pound's emphasis. Rather than being totally black and white about good and bad people, Pound suggests here that people can be improved little by little. In other words, he finds hope in the idea that people can become "a more living shell" over time, until they hopefully become not a shell at all, but a full-fledged human being capable of appreciating beauty and the best things about human culture.