The Insectrist skill is the test to make whether they can induce bugs or critters to act on their behalf. It is not a solid communication, but the artwork from David Peterson suggests those with a strong bond to one or more bugs can communicate in some manner.
As a GM, I’d have Apiarist handle bees, wasps, ants, and possibly termites. All are eusocial insects, but each presents different behaviors that are worth understanding. Termites are the least likely; they are cousins to roaches, so I’m not totally certain I would give the skill much effectiveness commanding clearly with them. Ants, wasps, and bees all respond to a queen, have castes of different roles in the host, gather foodstuffs back to the nest/hive, and tend to reduce numbers based on food availability and season. Ants are a critter I would place the lowest intellect, but highest degree of obedience. If the Insectrist can understand how to use scents correctly,t hey can command ants to do nearly anything imaginable. Wasps I would place in a middle-ground for intellect vs obedience; those who wake in Spring are fertilized females who immediately begin to build a nest for laying eggs. Hatchlings might be male or female, but males are the drone and hunter castes while females are hunters and may mate. The foundress remains the primary egg-layer, but her daughters can be fertilized and remain in torpor through Winter to start a new nest in Spring. So, it’s particularly balanced in respect to castes in the society, a new foundress does not compete for position inside the nest, but only in Spring begins her own nest independently. So, there’s some autonomy among wasps to ensure they can operate alone in Spring as foundresses. Bees have the queen and more rigid castes, so I’d place them under the more difficult to control vs intellect. The mice can gain a strong degree of obedience, but only if they ask bees to serve the queen, they cannot control the queen except my sugar-water or something like that. Also, the bees make honey, which is very useful–wasps and ants don’t quite offer that, though some make honey in small quantities (not for storage volumes). But, with the more diverse castes and roles, some bees are particularly idiots and others are particularly smart. There are more rigid rules about the hive as well, such as no drunkness (seriously, they’ll tear your wings off for that shit!), impeccable cleanliness, proper directions for food, no lying (liars die!). Among wasps, there is more independent spirit, with a social nest of eggs brooding and the primary chore is getting the larvae fed and growing. Among bees there is a caste for that, but not all bees need to learn it.
Also, none of the animals are making conversational friendships. It isn’t Redwall. The animals are wild beasts, the mice and weasels are civilized and settled. Personally, I use weasels to comprise stoats/ermine, ferrets, minks. Outside that are the cousins fishers and sables who are more wild, but can handle some meager sense of civilization when among weasel cousins. Then otters, badgers, wolverines are totally wild only, even as cousins of weasels.
For mice, I use mice to comprise a variety of mouse species, vole species, and rats. I do treat them all as much nearer the same size, so a bit of an evolutionary track that brought them closer in average size and allowed for easy cross-breeding. The nearest cousins are muskrats, beavers, squirrels, chipmunks, gliders, woodchucks, groundhogs, marmots. Those are willing to act with a meager degree of civilized behavior around mice, but are pretty much wild creatures. Rabbits and hares are allies with some civilization, but do not use technology, clothing, government, etc.
Anyway, Loremouse handles the matter of understanding and speaking with vertebrate beasts, such as beasts of fur, feather, skin, scales, fins. If it has a backbone and internal skeleton, that’s the domain of Loremouse. Insectrist handles invertebrates, but mostly pertains to arthropods. I let it handle worms, but I wouldn’t use it for some sort of “speak with ameoba” attempt.