Japanese beetles have been a real problem for me since we moved here in 2002, but I have found a method of therapy. I fill a large-mouthed plastic container (such as a mayo jar) 3/4 of the way up with water, and then add a few drops of dishwashing soap. I shake it up, and then go from plant to plant and sweep the beetles into the jar. The soap breaks the surface tension of the water, and the beetles can’t get out. I don’t know how effective this is, but it makes me feel better. :)
It’s very effective, just tedious. That was my usual method and when they were bad, I was out 3 to 5 times a day. Drowning them in plain water takes them too long to die which seems cruel. Plus like you said, they can climb on others and escape.
We have had good results with the hanging traps.