longhorn beetle grub
Refers specifically to the larva of the longhorn beetle (カミキリムシ), known for boring into wood. The name 鉄砲虫 (literally 'gun bug') may come from the sound it makes or its shape.
See also: カミキリムシ
The longhorn beetle grub tunnels inside the wood.
A longhorn beetle grub came out of the dead tree in the garden.