A Practical, Non-Technical Identification Guide to Common Terrestrial Arthropods →Based on traits observable with the naked eye when specimen is at rest. To use this guide, also called a dichotomous key, observe your specimen to answer question 1, then follow the direction “go to” to the next question indicated. Continue in this manner until identification is reached. Note that there are many taxa not included, so if your specimen does not match any of the answers it may be something else, such as a different group, a juvenile, or an unusual species (for example a “clear-winged” moth). A useful supplement to this key is Insects, Spiders and Other Terrestrial Arthropods by George C. McGavin (DK Smithsonian Handbooks, 2002) 1A. Has a segmented body with jointed exoskeleton and pairs of legs on at least some body segments……….Arthropod, go to 2. 1B Does not have jointed exoskeleton, may have hard shell with body parts extending outside of it or soft segmented body with slimy surface……….STOP, not an Arthropod, find a new specimen. 2A. Has 7 pairs of legs, obvious antennae, may be able to roll in ball……….Terrestrial Isopod (Crustacean) 2B. Not exactly as above……….go to 3 3A. Regions of body same, has more than 8 pairs of legs, with legs on each segment……….Myripoda, go to 4 3B. Regions of the body different, with legs on some but not others, some appendages may differ, may have wings……….go to 5 4A. Has one pair legs per body segment, flat body……….Chilopoda (centipedes) 4B. Has two pairs legs per body segment, domed body……….Diplopoda (millipedes) 5A. Has 2 body sections (head, cephalothorax), 4 obvious pairs of long walking legs on cephalothorax……….Arachnid, go to 6 5B. Has 3 body sections (head, thorax, abdomen), 3 pairs of legs on thorax, and may have wings……….Insect, go to 7 6A. Pedpalps (anterior to 1st pair walking legs) blunt, has up to 4 prs eyes……….Aranea (spiders) 6B. Pedipalps with chela (claws), has extended jointed tail with stinger……….Scorpiones (scorpions) 7A. Has obvious wings when at rest……….go to 8 7B. Does not have obvious wings when at rest……….go to 11 8A. Wings opaque, 2 prs (may be hard to tell), may be brightly or dull-colored……….Lepidoptera (butterflies,moths) 8B. Wings translucent……….go to 9 9A. One visible pair of wings………. Diptera (flies, mosquitos) 9B. Two visible pairs of wings……….go to 10 10A. Fore and hind ,wings same size/shape, wings and abdomen long……….Odonata (dragonflies, damselflies) 10B. Hindwing smaller than forewing (may be hard to tell 2 prs wings), abdomen rounded, thin “waist” between thorax and abdomen……….Hymenoptera (ants, bees) 11A. Has obvious cerci (non-segmented “tails” extending from abdomen) and does not have long, thickened femur……….go to 12 11B. Does not have obvious cerci and/or has long, thickened femur of hindleg……….go to 13 12A. Two cerci, large and shaped like pincers………. Dermaptera (earwigs) 12B. Three cerci of equal length, long and slender, body appears dusty……….Thysanura (silverfish) 13A. No wings, abdomen rounded, thin “waist” between thorax and abdomen Hymenoptera (ants & bees) 13B. First pair wings opaque and toughened (leathery), may not look like wings and held flat to body……….go to 14 14A. Has long, thickened femur of hindleg……….Orthoptera (grasshoppers & crickets) 14B. Does not have long, thickened femur……….go to 15 15A. Forewings opaque and hard, somewhat domed and meeting in straight line down back……….Coleoptera (beetles) 15B. Forewings leathery and flat, cover most of body, laying on top of one another at midline (may also have only stubby wings)……….Blattoidea (cockroaches) ©Bonnie J. Ripley 2020
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