While these count as larval stage of moths and butterflies, since you can tame them as hunter pets and they are never going to metamorphise into anything else, I'm going to give them their own section.
Caterpillars represent the larval stage of thousands of species and their color variation almost matches that of their adult stages. Since a lot of animals feed off of caterpillars, many have developed defense mechanisms to ward off predators. Some have hairy spines that deliver a toxin when touched. Others are brightly colored as a warning that they are poisonous to eat (some are, some aren't and are just cheating the system.)
If a moth can be a hunter pet, then a caterpillar can be as well. They are considered "silkworms" as hunter pets and grouped with Worms. Not sure I agree with that. Completely different phyla.
These guys are real insects that use water's high surface tension to literally "walk" on the water. There are about 1700 species and they live mostly in freshwater, preferring still ponds to moving streams or rivers. The environments where you find them in-game are just wonderful for them. Their movement over the water is perfect and I quite enjoy the inspiration Blizzard took from their wild counterparts.
I really like that they are mounts, so unique, and of course I'm always happy when they give us more hunter pets.
And then there's this guy...
This questline in the Valley of the Four Winds was a neat progression of meeting the people and building the skills to then punch this guy from the inside, after Miss Fanny hits you as hard as she can to get you into the belly of the giant bug.
The new insectoid sentient race - the Klaxxi.
They remind me of preying mantis.