"Ever since I was a little girl if I saw one, it would be a physical reaction and I'd freak out," Contactmusic quoted Mendes, as saying.
"If I saw one I'd have to have somebody kill it and then I couldn't take their word for it, I had to see the dead carcass.
"It was getting in the way and if I'd see one in the room at night... and someone couldn't get to it and it kind of got lost, I couldn't fall asleep in the room... It was psycho territory," she added.
Therefore, the actress visited a hypnotist and she has revealed that it really helped her to conquer her fear.
"You lie down, you relax and then she takes you through this kind of relaxation thing and then the cool thing is you think it's only three minutes and then the whole hour went by," Mendes said.
"I don't know what she did in there but it's helped. Now, I'll see one... and I'll just be like, 'Cool, what's up...?' and we're cool with each other," she added.