How do earthworms get into above ground pools?

I live in a neighborhood which abounds with above ground swimming pools. My best friend (which lives 3 houses down) and I have been perplexed as to how earthworms can somehow magically appear in our pools after a rain. He thinks that passing birds drop them en route to the cover of nearby trees, but I think there’s no way any bird worth its salt would part with such a tasty morsel. I considered that maybe they were crawling the four feet or so up the sides, but then I couldn’t figure out how they could get past the guard rails which are ninety degrees to the side walls. The deck is not touching the pool, and I’m not aware of any domestic leaping annelids.This one leaves me scratching my head. I’d really appreciate the straight dope on this one. How do those worms get in there?

If the surface is reasonably damp, the worms probably stick to it fairly well. They certainly seem to have no trouble getting up underneath the lid of my compost bin.

Even if the worms could crawl up the sides, why would they go into the water? Why would they “fall” on the inside of the pool when they didn’t fall off the outside.

I vote for dropped by birds. I’ve seen birds drop worms, fruit, etc. before. They usually just swoop back down and grab it again, but if it’s in the water–no dice. Unfortunate for Mr. Bird.

If you pick up a worm and rub your finger along it, you’ll feel that under its slime, it almost feels a little bit rough, kind of like a less-abrasive cat’s tongue. This is easier to feel on big worms than smaller ones. This helps the worm pull itself along. It works great when they’re going forwards, but doesn’t grip so well if they’re upside-down. It’s quite possible for them to fall into the pool once they’ve crawled over the edge.

In my experience, the insides of pools tend to be a lot smoother than the outside. And a worm in water is totally helpless - they can’t rely on gravity to give them grip, they can’t stick to a surface the way they would if it’s just damp, hence they can’t get any traction.