Two strange things on the pear tree

Two strange things on the pear tree

Observation - Two strange things on the pear tree - UK and Ireland. Description: My pear tree is covered in these little black things that look a bit like thin tadpoles - slimy looking and not moving. Presumably they must be a caterpillar of some sort but not like anyone I've ever seen before? The second photo is of the same tree. On

My pear tree is covered in these little black things that look a bit like thin tadpoles - slimy looking and not moving. Presumably they must be a caterpillar of some sort but not like anyone I've ever seen before?
The second photo is of the same tree. On the top of the leaf there is what looks like a rust spot and on the underneath, these udders have formed.
Whats going on!