Option C: As mentioned in the passage, "Some butterflies simply disappear by becoming exactly the colour of their host plant."
Some butterflies camouflage themselves by becoming exactly the colour of their host plant. They only appear to disappear, but instead change their appearance. The same is mentioned in option C, hence it's the right answer.
Options A, B and D: These lines are neither mentioned nor implied in the passage.
Hence these options are wrong.