Giant bugs are quite uninteresting compared to the chitin-clad, emotionless monstrosities they could be. In general, giant bugs are little more than vermin that have been sized up through RAW magic,but could achieve
so much more with specialized editing. I have some suggestions that would make them more flavorful and useful to the discerning fortress.
A lot of bugs and creepy crawlies have antennae. Antennae are sensory organs that function differently from bug to bug, but could function in Dwarf Fortress as a general nerve-dense bit of anatomy that could serve as a "weak spot". Destroying the antennae would have a disorienting effect. Bugs have mouths, but many of the giant bugs can't bite. Many bugs, like grasshoppers, don't seem to bite people all that much in real life, mainly because they're many many times smaller than us. But they definitely have chewing mandibles, which they use to eat grass. Bump up their size a couple of orders of magnitude, and they ought to be able to use those mandibles to chew on dwarf heads. More on the grasshopper (just as an example, I'm more of a fan of Giant Mosquitos), they have legs that, proportionally, are incredibly powerful. If that grasshopper is now donkey sized, proportionally speaking their legs should be able to kick a dwarf a mile or so into the distance. Other creatures will have combat skills tailored to their biology: Mantises with brutally powerful, agile strikes, Giant Jumping spiders having a fantastic innate jumping, ambushing and sensing skill and the ability to pin down prey while they attack with fangs.
Bugs also lay eggs, for the most part. If we were biologically accurate, there'd be game-breaking clutches of hundreds and hundreds of eggs, but average clutches would be less insane. A breeding pair of giant bugs would go from useless to a useful supply of meat, eggs and other animal bits. Life spans should be adjusted from a single year to multiple years - having young that goes from egg to fully-grown adult in a single year seems pretty imbalanced and it's basically psychological torture for anybody who would adopt a giant bug as their pet. I'm not sure if it's possible for RAWs to express life-cycle stages like larvae and pupae in an anatomical sense, so they'd be larvae and nymphs and stuff in name and tile only.
Giant bugs should be trainable to some extent. No war snails or anything like that, but let me tell you, I had a jumping spider in my window once and I'd drop it bugs and it would pounce on them in a blink of an eye. I feel like if that spider were still alive and also the size of a horse, he'd be a pretty darn good hunter. Predatory insects like giant mantises and spiders of all sorts should be able to accompany soldiers and hunters. Creatures who are obviously passive, like moths, should not be trainable as war or hunting animals though.
If you read that, thanks! I'm sick and it's summer and I'm just getting back into Dwarf Fortress so I'll probably dig into the raws and do some of this myself, but it would be great if these features were available to everybody.