Plane Sailing said:
For yick factor, how about the sea cucumber?
That has been done in Monsters of the Boundless Blue (and I totally forgot the spider eater when I mentioned the cicada-killer).
There are several ways to divide insects and the most basic is by their metamorphosis. The most primitive insects, the order that contains the silverfish, has no metamorphosis at all. The primitive winged insects, such as mayflies and dragonflies, has an aquatic immature form called a naiad that is similar to the adult in form- adaptations to living underwater determine the differences. Grasshoppers, termites and their kin have gradual metamorphosis, where the immature form is called a nymph (most look very similar to the adult). And finally there is the complete meatmorphosis of flies, moths, bees and beetles, the immature form is called a larva.
Some termites use their nymphs as workers (males and females) and adults as soldiers. Others have a seperate caste called the nastute that use chemical warfare by spraying sticky or toxic fluids (Antz had these).
Unlike most vertebrates, insects have little or no inbreeding depression. A single fertilized queen yellowjacket is the ancestor of all yellow jackets on New Zealand.
Immature spiders of many species travel by ballooning- they climb something tall near their hatching spot and emit a line of webbing. The wind catches the webbing and floats the spider away. Islands that have been devastated by volcanic eruption will have spiders before any other terrestrial organism.
Thrips are a order known mainly by gardeners. They are tiny insects with feathery wings that can kill large plants with very few numbers. A treant infected with dozens of 1/8th inch long thrips could die from them.