My four year old son...was coloring on a piece of paper at his color table...the paper flew to the floor and he jumped up on top of the chair...screaming "SPIIIIIDDDDEERRRRRRRR"...thank goodness for his almost 7 year old sister she came to the rescue...but he refused to get down off the chair until we proved it was dead. I know it's a common "fear"...but between ants and spiders my son screams and cries.
I don't get it...because this is the same boy who wanted to jump from our deck into the trampoline (enclosure)...yes into meaning the deck was an high as the enclosure and he wanted me to let him jump into it! (BTW not hate PMs I did NOT let him do it)
ETA: My almost 7 year old daughter...I'm not sure she's really afraid of anything "unusual".
My cousin who is the same age as my daughter though would freak out when in a public restroom the auto flush would happen...screaming, crying, hysterics!