Possibly scale, check the branches and see if there's a little, hard, bug infestation that's hard to remove, though you can flick them off with your finger nail sometimes. If there is, there's also likely to be ants travelling up and down the tree, they 'milk' the scales for their secretions. 'White' oil is the treatment - it chokes the bug and prevents it from sucking. You should also apply a ring of petroleum jelly around the base of the bush to stop the ants. I sometimes use a commercial insecticide but a lot of gardeners believe that's a no, no, now-a-days on account of possible damage to friendly insects.

I would say by the looks of it the image, it is a species of spider mite there are around 1200 species of spider mite.

Spider mite are systemic insect in that case you will need a systemic insecticide you will pick up one from your nearest nursery

ps. can also give your lily pilly a spring time cut if you want to, and disposes of the pruned spider mites leaves properly.

regards
Benjamin Manning
Canelands nursery

Yes Ben, I think you're right there, the web-like structure does point to that conclusion.

Thank you Ben and Funnelweb!

I have been giving the leaves a spray of water and that has helped so I assume it is spider mites.

Today I have noticed something that looks like it maybe wooly aphids or mealybugs. The plants do have ants all over them so could be either. Hoping the ladybugs I've purchased will help.

Thank you again :)

Don't think the ladybugs will eat the ants born_free, sounds like you might also have scale. I'd try what Ben suggested, a commercial systemic insecticide, used with caution it'll not cause too much harm to the 'goodies' on the plants. Also I'd try a ring of petroleum jelly around the base, that should stop the ants and interrupt the cycle where they 'farm' scale bugs.