That's foolish talk. They don't have to DISBELIEVE, according to your earlier statement. I daresay you had never had an opinion on the psychic nature of spiders until I brought it up, there for you neither believed nor disbelieved. Ergo, if they have psychic abilities, then your failure to believe in them was inconsequential; whereas if they did not have psychic abilities, it could not have been due to an active disbelief on your part, as none existed.
And that doesn't even BEGIN to approach the problems of opposing beliefs, and doesn't even touch the arguments about whether you actually can DISbelieve something or simply believe in an opposite worldview. It also doesn't bring up the complication of kids who jump off roofs getting injured by hitting the ground despite their very real belief that a cape will enable to fly (note that it is the injury that ends the belief, not the end of the belief that causes the injury).
Therefore, the "if I believe in it than it is real" theory is false.
Therefore, Spiders are psychic and are probably plotting to suck your brains from your head as we speak.