Both species gang up to devour everything they can find, spreading ruin. According to this article, being part of the devastating horde triggers the development of the brain in one species.
This phenomenon has never been observed in Washington DC, where the ravening swarms of the other species are most often found feeding.
The major difference is that locust don’t pretend they’re doing you a favor.
My favorite locust story comes from “Things Fall Apart”, a book by Chinua Achebe (1958) in which a Nigerian family (1 man, 3 wives, many children) fight to survive durig a drought in Niger. First hunting fails. They defend their garden from wild animals, thieves, and search for water to keep the plants alive. Finally, at the end of the book they see a black cloud on the horizon coming towards them. It is not rain. It is a swarm of 30,000,000 locusts. Is their crop lost? Yes. Do they starve to death? No. They get fat eating locusts.
Sometimes, when a swarm runs out of food, the locusts eat each other. This sometimes happens with politicians for the same reason.