content: I would say it's mostly conditioning that people are afraid of bugs.  I'm always giving my 8 and 4 yo daughters "icky" things to hold, and they're not bothered, however if I haven't done it for a while they get hesitant.  They learn from their classmates and friends that bugs are gross so it's an ongoing battle to fight peer pressure.  I also teach them to be cautious when encountering something new since some bugs can cause damage.