Root tips disappearing - chewed off!

[lepetitmartien]

If the snail is big enough, you'll see teeth marks.
A caterpillar will "regularly" chew, making his diner from one position then moving a few steps and resuming (those on leaves are a good example)
Insects like cockroaches (or else) will nibble irregularly. it'll be munched, chewed on, no clean cut.

Anyway, you have some serious chase to make.

Maybe if it's cokroaches you can use plaster/sugar - mix of powder only- or borax/milk concentrate -this one makes little balls- sweets (if the place is adequate, dry enough, and not accessible to kids/animals), they nibble on and die of plastering.