AnimalsArthropods — Phylum Arthropoda
Animal with an exoskeleton, segmented body, and jointed appendages.
Quick links: butterflies, dragonflies, lady beetles, grasshoppers, spiders

Insects
Insects — Class Insecta
Six legs, head, thorax, and abdomen. Flies or crawls.
Arachnids
Arachnids — Class Arachnida
Eight legs. Crawls.
Millipedes
Millipedes — Class Diplopoda
Two legs per segment. Crawls.
Common Pillbug
Crustaceans — Subphylum Crustacea

More information

Unless otherwise noted, we are following BugGuide.net for taxonomy of arthropods. We would have liked to use ITIS as the exclusive authority on taxonomy, unfortunately it is lacking many entries for insects and spiders.
Resources: