One of the best ways of raising funds for the little outback school in which I worked in South Australia was to go stump-picking. After a farmer had cleared an area of land, the roots of the mallee trees would remain under the ground. These would have to be removed before the soil could be worked.
The mallee has a survival adaptation in which it forms a lignotuber. This is something like a giant, knobbly potato made of wood. It is composed of stem (rather than root) tissue and forms a mass of woody storage cells from which the several trunks project upwards and the erosion-resistant roots go down. The fat stored in these tubers means that a lot of heat energy is released when the mallee stump is burned. They make really good firewood and can be sold for a good price.
Every so often, members of the school community would gather at a recently cleared paddock and begin work, hoicking the mallee roots out of the ground and chopping them into manageable lumps for transport and sale. Occasionally, one’s axework would reveal a white grub between 8 and 12 cm long. This was a witchetty grub, the larva of what was locally known as the rain moth. On the rare occasion that we had heavy rain in the mallee region, we were likely to be invaded by a flock of these enormous moths, as big as a sparrow and hopeless at navigation. They would flap about, bumping into things, mating if they were lucky and laying eggs in the mallee trees to start the cycle off again. If you left an outside light on during one of these episodes, you would have a drift of dead rain moths to dispose of the next day.
The witchetty grubs themselves are eating machines. They use powerful jaws to chew tunnels through the mallee roots. Their digestive systems have the enzymatic combination required to digest wood into sugars and release the stored fats for their metabolic wizardry. They were our little treats during a hard day of stump picking. When I found one, I would hold it by the head, avoiding the efficient wood-boring jaws and bite the body off. They taste like a sort of savoury custard with a lovely, nutty flavour.
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