There are various appendages gathered from insects that are prized as beneficial, as long as you're extracting the correct part; avoid a disappointing conclusion to combat with a giant wasp in the swarms of Black Marsh by harvesting its eyes, mandibles, and ovipositor, leaving its thorax, wings, and any other aspect to rot in the wilderness. All other insects that feature the aforementioned parts are useful to the enchanter, but similar body parts from other creatures, such as the mandibles from a dreugh, aren't of interest in this instance.