AKA Jumping Plant Lice, these particular psyllids are tiny builders that extract sap from leaves (they have sucking mouthparts like all true bugs) and instead of feeding the resulting waste product to ants in return for protection, they build little coverings called Lerps to hide in until they develop wings. Maybe they just don’t like ants. Whatever, sooty mould loves Lerp honeydew and can end up causing leaf drop and killing the tree. So love your Lerps in moderation. They come in all sorts of shapes and sizes and you’ll find them on gum leaves, go and look now!