My lemon tree, ants, shells. What is this and how to treat it properly?

Question

There are lots of ants around, they just don't like to be photographed :)

This is the whole tree:

I'm in Sydney, Australia.

Answer 1

It appears to be scale insects.

I'm not experienced with scales, but I imagine you can use neem oil and/or diatomaceous earth once in a while to help. I would get the diatomaceous earth all over the stems, wherever they are. I hear you can put a circle of cinnamon or something around your pot to help deter ants.