Spiders
Snakes
Rats
Mice
Actually bats don't frighten me at all. We used to to out at night and watch them fly around at my grandparents. We don't see as many now, but my sister and I were both thinking of building and installing bat houses (kind of like bird houses) so that more bats would come around and eat the mosquitos.
I love watching the big fruit bats at AK, too.
But, now a spider will (and has) cause me to leave the house if I don't have anyone handy to get rid of it for me.