You're going to have to do some adventuring to find Grub Hide in Grounded. This is more of a mid-stage item, because you'll need to make your way over to the big acorn tree that can be found deeper into the map. However, quite a few recipes require this resource, so you're going to need to get there eventually!
To get Grub Hide in Grounded, you will need to craft a shovel, head to the acorn tree, find Grubs burrowing in roots, dig them up, and kill them for their hide. Grubs can only be found in dark areas in the mud, you will be able to see them moving around because the dirt shifts.
Make sure you have a hammer of some kind before you head out on your adventure to the acorn tree. We will need it to break the walnuts and collect their goods. You'll also want to have at least a couple of sprigs and one woven fiber. If you want to play it even safer, have a spear and maybe even a bow along for the ride because there's some mean bugs in this area.
If you have Arachnophobia, now would be the time to play with your safe mode settings because you could run into a not so friendly spider soon.
Either get on top of something, or look around the sky for the big tree with the red leaves on it. That's where we need to start heading off to get ourselves some Grub Hides.
Make your way to the tree, and try to avoid any bugs along the way. You will eventually reach the base, and see a bunch of roots running around the ground. Look for Acorns that have fallen from the tree, take out your hammer, and then smash them open.
Collect all the pieces that break off from it, we will likely need some of it later. For now, we really just need one shell. Once you collect it, open up your crafting window and make the Acorn Shovel. We've got the shovel, now we need to find the Grubs. Look around dark shady places around this tree. You will find little dirt bubble trails in the dirt and on the roots around this area. Once you see that, take out your shovel and dig up the Grub.
This will pop the Grub up and you can kill it with whatever you like. Once you have just loot the Grub and you'll get yourself a Grub Hide!
You can use this hide to create yourself a Canteen, Mite Hat, Grub Vest, and some other stuff further down the line!