Phylogenetic tree of insect orders, after Wheeler et al. . Light gray, Archaeognatha (primitive wingless insects); Dark gray, Paleoptera (primitive winged insects); Black, Neoptera (higher insects). Crustacea are shown as an arthropod outgroup. Thysanura include silverfish; Odonata, dragonflies; Orthoptera, grasshoppers and crickets; Phasmida, stick insects; Blattaria, roaches; Heteroptera, true bugs; Homoptera, aphids, scales and tree hoppers; Coleoptera, beetles; Hymenoptera, ants, bees and wasps; Lepidoptera, moths and butterflies; and Diptera, flies.