These creatures mimic the shape of desirable and mundane items adventurers often com in contact with. The most successful ones take the shape containers with the promise of valuable treasure to be had. They lay in wait for a greedy unsuspecting adventurer to rush for the prize, instead finding their arm shoulder deep in the maw of a vicious predator. When they spring their trap they ooze out sticky ichor which allows it to adhere to the prey and any martial weapons used against them.
Once one has encountered one they'll never look at inanimate objects the same, building a healthy helping of distrust for any adventurer looking to stay alive.