Spidey powers? ha kidding

I'm assuming the use their mucus secretions to adhere to walls or perhaps they use the surface tension of the water on bin to provide grip to climb

californian and takadi,

To move by sticking out there setae (little hairs) and contracting their body. I suspect that they climb using the same motion. Even if the pails seem smooth to us they may have enough rough surface for the earthworm to move.

Here is a link that might be useful: earthworm locomotion

Thanks for the answers. My next question is why do they do it? It always happens when its raining, so I assume they were trying to escape the water on my patio so climbed up the nearest object which was my bucket and fell in, and drowned anyway. Or were they purposefully trying to get to the water, somehow sensing there was water in the bucket? I have seen some that were still alive at the bottom of the water? Can earthworms live underwater, at least for a while? And why do they always go on concrete when it rains, why don't they just stay where they were or just go onto the surface of the soil?

I found some articles that partially answer my questions. For one, depending upon the types of earthworm they can live underwater for 13 to 96 hours.

http://snailstales.blogspot.com/2008/06/why-do-earthworms-come-out-of-soil.html

http://www.moscowfood.coop/archive/earthworms.html

http://www.associatedcontent.com/article/464344/shower_of_worms_the_flying_earthworms.html?cat=47

http://www.newton.dep.anl.gov/askasci/zoo00/zoo00370.htm

http://ask.metafilter.com/29996/Earthworm-Toilet-Love

http://www.wormcity.co.uk/wormcity1.pdf