Why do you call sparrows the four pests-

That's the old almanac! Because people didn't know enough about sparrows in the past, they mistakenly thought that sparrows stole food, which led to a reduction in grain production. In fact, the sparrow steals only a small part. There are many sparrows, which will have a certain impact on grain output, but more importantly, it can eat many pests, which people didn't realize before.