Hello Zoë,
" Katydids are primarily leaf-eaters, although they do munch on an occasional bug if they can catch one. "
This reference says that Katydids are primarily carnivorous.
https://feedingnature.com/what...
Notice that the zinnia in your Katydid photo hasn't been chewed on. I have seen a lot of Katydids on my zinnias, but never any evidence that they have taken even one bite out of a zinnia bloom, or zinnia foliage. I have never seen a Katydid eating any kind of foliage. So I don't consider Katydids to be a "bad" insect. I do consider Grasshoppers to be bad. Apparently, there is a difference of opinion as to whether Katydids are herbivorous or carnivorous.
ZM
