The witchetty grub (also spelled witchety grub or witjuti grub) is a term used in Australia for the large, white, wood-eating larvae of several moths. In particular, it applies to the larvae of the cossid moth Endoxyla leucomochla, which feeds on the roots of the witchetty bush (after which the grubs are named) that is widespread throughout the Northern Territory and also typically found in parts of Western Australia and South Australia, although it is also found elsewhere throughout Australia.

The term may also apply to larvae of other cossid moths, ghost moths (Hepialidae), and longhorn beetles (Cerambycidae). The term is used mainly when the larvae are being considered as food. The grub is the most important insect food of the desert and has historically been a staple in the diets of Aboriginal Australians.