Distinguishing Insect Relatives

One of the necessary skills in integrated pest management is the ability to make accurate pest identifications.  For insect pests, that starts with the talent to distinguish insects from their close relatives.

"All insects are arthropods, but not all arthropods are insects."

Insects and their relatives are animals, and they are members of the Phylum Arthropoda.  Arthropods are by far the most successful animals on the planet. They have conquered land, sea, and air and make up over three-fourths (80%) of all currently known living and fossil organisms. 

Arthropods are distinguished from other animals by the presence of an exoskeleton (a rigid, protective covering around the outside of the body) on a segmented body that possesses jointed appendages such as legs, mouthparts, and antennae.  This presence of jointed legs gives the Phylum its name (Greek arthros=jointed, poda=foot).

There are about 15 different groups of arthropods (it depends on how you count!).  The five we commonly encounter are Arachnids (spiders, ticks, mites); Centipedes; Millipedes; Crustaceans (shrimp, crabs, lobsters, sowbugs), and Insects.  The principal external characteristics that differentiate the types of arthropods are the number of body regions, the number of pairs of legs, the number of antennae, and the presence of wings.

Adult Characteristics of Common Groups of Arthropods



  • 3 body parts (Head, Thorax, Abdomen)
  • 3 pairs of segmented legs
  • 1 pair of antennae
  • 0, 2, or 4 wings


spiders, mites & ticks

  • 2 body regions
  • 4 pairs of legs
  • No antennae
  • No wings
  • Simple eyes only


lobsters, crabs, shrimps, barnacles, sowbugs

  • 2 body regions
  • 7 - 19 pairs of legs
  • 2 pairs of antennae
  • Nearly all are aquatic (exception: sowbugs)


  • Elongate, flattened body
  • 15 or more pairs of legs
  • 1 pair of legs per body segment
  • First legs = poison jaws
  • 1 pair of large antennae
  • No wings


  • Elongate, wormlike
  • 30 or more pairs of legs
  • 2 pairs of legs on most body segments
  • 1 pair of small antennae
  • No wings




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