I am fairly sure those a slugs/snails. The chew marks are most likely from the outside as they would probably slide in if they were going to eat from the inside.
I would walk outside a couple hours after dark and check to see if some slippery bugger was sliding across your plant. I don't know if slugs/snails are prolific in your area. If they aren't, then manually remove the slug and end it with a quick knife slice. Try not to touch a garden slug, though. It is not a very fun experience
I had issues with wasps chowing down on some of my flytraps (last year), even if they weren't being caught in the traps.
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