1) One of the things I've noticed about nature shows is that what really weirds people out is when "lower" life forms eat nominally "higher" life forms, especially in creepy ways. If you've ever seen a large spider eat a bird, you know what I mean. (See also 3, below)
2) Anything that liquifies its prey in whole or in part, especially from the inside out, is a guaranteed creepout. Mostly, you're talking land-based arthropods- spiders, scorpions, flies, etc.
3) Anything that eats its live prey whole...sloooooowly...creeps people out. Most people would think constrictor snake first, but they don't do the live part. Cone Snails, OTOH, use a harpoon-like radula to inject a nonlethal paralytic poison into small fish (and other prey) and eat them whole. I used a Giant sized one of these in a campaign once...the hate of the thing was almost visceral.
2) Anything that liquifies its prey in whole or in part, especially from the inside out, is a guaranteed creepout. Mostly, you're talking land-based arthropods- spiders, scorpions, flies, etc.
3) Anything that eats its live prey whole...sloooooowly...creeps people out. Most people would think constrictor snake first, but they don't do the live part. Cone Snails, OTOH, use a harpoon-like radula to inject a nonlethal paralytic poison into small fish (and other prey) and eat them whole. I used a Giant sized one of these in a campaign once...the hate of the thing was almost visceral.