The Giant Wood Moth is the heaviest moth in the world, with some females weighing up to 30 grams. The caterpillars of wood moths feed on plant roots, but the adults do not feed during their short life span.
The larvae of some species of wood moths are better known as witchetty grubs and bore into smooth-barked eucalypt trees. As they grow, the tunnels left behind in the bark increase in width. They may spend up to one year within the tree before emerging as moths. The newly emerged, small caterpillars lower themselves to the ground on silky threads where they are thought to feed on plant roots. As adults they are unable to feed and only live for a few days. The heavy females lay about 20,000 tiny eggs before dying.
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Info via Australian Museum