The existence of animals in Belobog :
Definitely exists :
Scorpions
Crabs
Olm
Funeral worm
Lizards
Moles
(All are well-documented in encyclopedias)
Plains Bear Cub (just straight up there)
Cows (Moo-Moo Milk)
Snapper (Snapper Jam Appetizer)
Salmon
Butterflies
Bees
(The Goethe Hotel serves Salmon Cheese Tart, Honey and Oats Mousse and Butterfly Berry Tart)
Mice (Vache experimented on them and Natasha even kept them as pets as a kid)
Chickens (Musicians of Belobog, but there are other evidence of it existing)
Extinct : Tri-toothed beast (Mid-terms)
Inconclusive :
Serval/Lynx/Gepard (The siblings never mentioned them being named after animals. Theoretically possible for their parents to choose these names without the animal actually existing. There are ppl irl named Griffin)
Pigs (The item description for Belobog says they are most likely pork, non-zero chance it’s not)
Owls (only evidence is Bronya’s Snow Globe, toys based on fictional animals are rampant irl, case and point : Pokemon)
Donkeys, Cats, Hounds (Musicians of Belobog : in-universe fictional story, no other evidence)
Moose (Horn Of Snow ascension mat, no other evidence)
Termites, Sandfox (places named after them, there are places irl named after mythological creatures)
Paradoxical : Birds/Pigeons (Natasha’s not aware of their existence but Goethe Hotel serves Poached Eggs, could be reptiles’ eggs, Belobogians eat mole so reptile eggs aren’t that weird)