With me, fear of spiders seemed to start with IIRC my mother's reactions to seeing them, likley in camping trips when I was around 6 or so, or the daddy longlegs (harvestmen) you would see when turning over a rock in the woods, or even in the backyard. But that's funny, as she used to scream at anything, like the common roaches in the house, though they didn't become a problem until I was older. But with the spiders and harvestmen, it's something about the way they move; the prominent legs, and also webs being icky.
So now, when I should be getting over this, I have this wife who's extremely afraid of spiders (can't even see a picture of a big one), and for even the wispy little ones in the house occasionally, I have to be alarmed by a scream which just shoots my adrenaline up and not knowing what I'm going to find when I go in there. (While my mother says she sees spiders in a garden, and seems to think nothing of them now).
So it seemed for me to be tied to some inferior Fe reaction, but it doesn't seem to correlate perfectly. I always think they're so little and we're so big, so the fear is irrational, but it seems to be very ingrained (and it would be similar for other very leggy insects, or weird ones like the sticks or leaf. And if anyone knows [MENTION=179]iwakar[/MENTION] on FB, you should see the weird thing she posted from her door post just this morning). I wondered if Trickster Se or ASD could be involved, but again, it doesn't seem to be type-stack specific, and no studies have been done on this.