A Grub in Antwar.io is a type of bug that is a food source throughout the game. They spawn randomly Underground. They are usually surrounded by Dirt, although sometimes they spawn in open spaces. You never actively see one spawn, unlike the Beetle and Anate. Also, they can be found in all 4 seasons. They are a good source of food, especially when you have just claimed your nest.
Grubs do not have any movement speed or damage, making them easy targets for Ants. They only have 60 health compared to any other Bug's 100, meaning they can get picked off in 12 hits by a Nanitic and 8 by a Worker.