My worst fear - mice and rats.
I've read logs where other cachers have discovered a rat looking at them or stuck their hand in a hole and been bitten by something. Bah, I thought, it wont happen to me.
I took Little QC up onto the Ridgeway this week. We did a few caches, but the going was tough; snow and ice don't make it easy to push the buggy. We came across one cache, it had a nice hidey hole in the top of a fence post. I removed the cache and "eeeeeeek" lots of little mice looked up at me. I dropped the cache in surprise, swore a bit, quickly replaced the cache and ran away! I had to go back as I hadn't signed the log. I wasn't touching the cache again so took a photo of the hide, I used the zoom so I didn't have to get too close to the mice!