wait.... if the Mother Grub the same species as the trolls? I don't understand how it is able to even give birth to trollss

The Mother Grub is a Lusus Naturae, but I mean Trolls have incredibly volatile genes and the Lusii are all apparently a similar species enough to fall under the same category, even though they vary wildly from one another. You could consider the Mother Gurb as a sort of ‘Queen Troll’ of sorts, wildly different but technically the ‘same species’ so to say?

Or you could consider the Mother Grub a Host. I personally headcanon that Trolls have a sort of parasitic, symbiotic relationship with Mother Grubs, and that they’re just using them to produce their spawn. You’d have to ask Hussie about the details of Troll Reproduction.