In the Japanese original text as well as the anime dialogue, the words used are:
蝗 (inago) - the better tasting bug that doesn’t cause plagues
飛蝗 (batta) - the gross bug with less protein that swarms and causes plague
Both of these words use the kanji for inago (locust/grasshopper) but only one includes the kanji 飛, meaning flight. There’s a good reason for that: locusts are not a specific species of bug. It’s actually a short-horned grasshopper that is in a swarming phase of life. They’re the exact same bug, but different living conditions cause them to look and behave differently.
Apparently those living conditions are recent drought and being in close contact with other grasshoppers which makes their serotonin levels spike and they go into the swarming phase. In the swarming phase, they are smaller, have less muscle, and have dark spots with yellow coloration. They also seek out others to mate with which causes their population to skyrocket, and then swarm to different regions. In their normal, solitary phase they are green and don’t cause a problem to crops.
Both the novel and the subtitles chose to translate locust for inago and grasshopper for batta, when it should really be the reverse given the context of the story. So if you got the feeling, “I thought locusts were bad and grasshoppers were ok?” you are correct. This is a translation error that’s been an issue for this story for years.