Savage Species has the Insectile Creature template, and Underdark has the Arachnoid Creature template. Arachnoid can only be applied to animals and magical beasts, so make them some sort of heavy guardians or just predators that hunt the insectile creatures and anyone else they find.

I'd use Insectile with any Jungle race, preferably something small size. They would have their broods underground but have surface settlements for agriculture. For the arachnoid creatures, Arachnoid Girallons would be absolutely terrifying, with eight claw attacks and a venomous bite.

They could use a pheromone pod or similar to control swarms of non-sentient monstrous insects or even stirges against their enemies. Make them use Giant Bombadier Beetles as mounts maybe, and/or have some advanced to large size to use as beasts of burden.