Something growing on the tree

I was walking a friend’s dog by the river this afternoon- she is away. The mosquito’s were terrible. At one stage I slapped at my arm and killed 3 mozzies in one go.

I noticed something in the bark of this tree. I couldn’t stand still for too long to study what it was because the mozzies were just too thick. I’m thinking it is an insect or moth, or possibly a fungus.