[Pictured: cossid moth larva (endoxyla leucomochla), also “maku”]
Technically speaking, there's only ONE true "whitchetty grub" and you DON'T find them in the trunks of trees. Originally named for the witjuti bush (acacia kempeana) of Central Australia, “witchetty” refers MOST appropriately to the large, white, wood-eating larva that feed through the core of witjuti bush ROOTS, and can reach up to about 5-inches long and about an inch around.
The name comes from the Adynyamathanha (Australian people) words “wityu” (hooked stick) and “vartu” (grub), which Europeans later renamed "whichetty." They're also called “bardi” grubs by freshwater fishermen along the Murray River, "witchetty" often applies to the hepialid moth larvae of trictena and abantiades, in fact, it's a term that CAN apply to thousands of similar-LOOKING, wood-eating grubs/larva like ghost moths (hepialidae) and longhorn beetles (cerambycidae).
Normally, they are hunted/dug for by women, but as you may recall, the tell/sign for Les Stroud was a bulge in the tree trunk, but true witchetty grubs are usually about one to two-feet below the ground at the base of the wijuti bush where the dirt above is often cracked, indicating an enlarged root where the grub can be found.
Other tells are the casings of the insect, or the excreted wood “poop” and or small hole in the tree trunk. Once caught, the grubs may poop a brown juice.
So yes, Les Stroud found his in a tree trunk, probably the red river gum (eucalyptus camaldulensis), which was likely a different species, but apparently good tasting nonetheless. They can also be found under black wattle trees and are attributed as the reason why wattles die within 10 to 15 years.
Witchetty grubs are so sought after and prized that they are often featured as “dreamings” in many Aboriginal stone paintings. A staple in the diet of Aboriginal Australians, they are an excellent “survival” food, being high in fat and protein (about 19.2% fat, 15.1% protein, about 100mgs thiamine and 5mg vitamin C per 100gms, they're also a valuable source of vitamin B1 and essential minerals like potassium, magnesium and zinc) which is why the Aboriginals seek them out (crushed, they’re even used for burns and wounds), here’s how they compare to a few other foods:
Beechnuts (4oz) = 644 calories, Acorns, white oak (4oz) = 568 calories, Witchetty grub (4oz) = 371 calories, BEEF ground lean (4oz) = 301 calories, Raccoon (4oz roasted) = 290 calories,
However, some species are as high as 33% fat and even 67% fat! Raw/live, they have a gooey, yellow inside that tastes “almondy” and/or “eggy” (like most insect larva i.e. ants, bees, wasps, etc.). Roasted, either on or over hot ashes, the skin becomes crisp like roast chicken while the inside becomes light yellow.
They CAN taste like crunchy-fried "peanut butter" or fried eggs and they "fry/sizzle" because of the high fat content. Or, you can try witchetty grub cappuccino, made with witchetty grubs blended with milk and sprinkled with wattle seeds (the drink has a slightly nutty taste).