The witchetty 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 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 Cossidae, the cossid millers or carpenter millers, make up a family of mostly large miller moths. This family contains over 110 genera with almost 700 known species, and many more species await description. Carpenter millers are nocturnal Lepidoptera found worldwide, except the Southeast Asian subfamily Ratardinae, which is mostly active during the day.