Hop Dog Photobombed By An Ant

I spotted this caterpillar under a hawthorn leaf. I have never seen one before but thought it was one of the Tussocks because of the tussocks of hairs on its back. I have Blipped the Rusty Tussock or Vapourer in the past.

When I touched the leaf it was on the tussocks parted revealing the caterpillar's black skin. It startled me. It looked to me like a gaping mouth. I wonder if this is defensive or threat behaviour?

I was careful not to touch the larva as the hairs can cause severe skin rashes or even a hypersensitivity reaction.

This is a Pale Tussock, they used to be known as hop dogs as they were often found on hop vines. As I was togging it an ant ran into shot carrying its swag. :)