what are these insects on the cuke plant? kill or leave them be?

[tnkrer]

I am seeing these jumping insects on the cuke plants. If you try to touch them, they suddenly jump to a new spot. They are brown, small with some weird fluffy stuff hanging from their back (or front, not sure). They seem to be on leaves and stem and not on the fruit. Do they cause harm to the plant? How bad?
Do these need to be eradicated? If so, what will work against them?
Thanks ..