I came across someone describing a Nihon yamori / gekko as a 益虫, and using "useful insect" in English. Gekkos aren't insects, but it made me curious what it actually does mean.
jisho.org only describes 益虫 as meaning "useful insect". The English edition of Wiktionary lacks a description of 益虫, has a terse description of its antonym 害虫 (harmful insect), and a slightly longer definition of 虫, but not one that'd cover gekkos.
What kind of organisms would be covered by 益虫, 害虫, or 虫, and what kind of animals wouldn't be covered by 虫?
(BTW: I'm aware that English has words for non-monophyletic groups, so no mockery is intended)