Question
I have a customer in the Charleswood area in Winnipeg, Manitoba, Canada.

she has a willow tree on her property and has an insect in which she describes as (black, smaller than a lady bug, round shape, when you squish it, it is red, attacks leafy branches by sucking the juices and in turn secreats a very sticky substance) "sounds like aphids, but this attacks the branches".  She says there are litterally thousands on 1 small branch and move from branch to branch after they are finished.

hope you can help, thanks

Answer
It sounds like the lady bugs are eating the aphids which is what they do. Lady bugs come in many colors not just red/black spotted some are solid black ot dark colored. IF there are as many as you say the lady bugs should control the aphid population or you could spray the tree with an insecticide and kill the aphids and the lady bugs. This late in the year I would let the lady bugs do their thing.