These little chewing creatures were on an acacia leaf. They were less than 1cm long and were on both sides of the leaf, working their way down and skeletonising it as a group.
Your excellent photo shows a group of sawfly larvae with black heads and tapered tails. They will grow into wasp-like insects.
There are many sorts of sawfly grubs. These have a tapered tail, unlike the better-known “spitfire” types.
They look like melaleuca sawfly caterpillars, although your caterpillars are on a wattle. Like the large “spitfire” type of sawfly grubs, they eat just one surface of the leaf when they are very small. As they grow, they eat both surfaces, skeletonising the leaves, leaving just the veins. Larger grubs consume the complete leaf.
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