Ever have ants invade your kitchen cabinet and get into all the food? That happened to my parents a couple of times. The only way I can imagine it happened is that they came up through the floor from the crawlspace. (Would that have happened if there was a finished basement down below instead?)
Another honorable mention is once when I was at a bonfire with some of my Trekkie friends. I helped gather firewood and, when turning over one log, suddenly there were hundreds of big, red ants scattering in all directions (the size of carpenter ants, though I had always thought carpenter ants were black).
And then, the time a wolf spider made an appearance in the break room at work. I've never seen so many adults act like such wusses in all my life. They were all trying to kill it but (good for it) it went inside the tubular steel frame of one of the tables. Lunchtime was over and everyone had to go back to their desks, so the spider was spared. (I mean, come on! About half those people were engineers.)
One more thing worth mentioning... the time a huge beetle got on a friend of my brother's. It was big like one of those black beetles, but its shell was pale green with spots like a ladybug. (Never seen anything like it before or since.) My brother's friend was no wuss, third-degree blackbelt and been in many fights, but this thing scared the shit out of him, to the point where I was like "All right! Hold still for a minute." while getting this creature off his sock.