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For Insects, Spiders & Their Kin
For the United States & Canada
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Class Insecta - Insects

leafhopper nymph? - Oncometopia orbona Moth caterpillar on oak - Protoboarmia porcelaria Banded Tussock Moth - Halysidota tessellaris Paonias myops - Small-eyed Sphinx - Paonias myops - male - female Asilidae Robber fly - Proctacanthus - male Beetle - Sesaspis emarginata
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Other Common Names
bugs
Spanish: insectos, insecta
French: insectes
Explanation of Names
Latin insectum, pl. insecta "cut into, cut up" (refers to body segmentation), a literal translation of Greek entomos (εντομος)
Numbers
Worldwide, 25-30 extant orders (+ ca. 10 extinct), depending on authority, up to 1000 families, and well over a million species
In our area (US & Canada): 28 orders, over 600 families, ca. 12,500 genera, and >86,000 spp.(1)(2)
Identification
Three pairs of legs
Three body parts: head, thorax, and abdomen
typically two pair of wings; some groups have one pair or none
One pair of antennae
Usually one pair of compound eyes; simple eyes (ocelli) present in many groups

Anatomy
See figures:
   
See BugGuide Glossary for terminology.

See Overview of Orders of Insecta--an illustrated guide to the orders of insects.
Range
worldwide and throughout North America (NB: aquatic marine forms conspicuously absent)
Life Cycle
There are two prominent types of life cycles among the insects:
Hemimetabolous insects (e.g., dragonflies, mayflies, true bugs, grasshoppers) undergo gradual, or incomplete, metamorphosis. Immature stages (usually called nymphs) go through a series of molts, gradually assuming an adult form. Since the wings develop on the outside of the body, these groups are called exopterygotes. Some orders have immature stages that are aquatic. These possess specialized structures for aquatic life, such as gills, and are called naiads, or larvae.
Holometabolous insects have a four-stage life cycle: egg, larva, pupa, and adult (imago). The following orders of insects are holometabolous:
Neuroptera - Antlions, Lacewings and Allies
Coleoptera - Beetles
Hymenoptera - Ants, Bees, Wasps and Sawflies
Trichoptera - Caddisflies
Lepidoptera - Butterflies and Moths
Mecoptera - Scorpionflies, Hangingflies and Allies
Diptera - Flies
Strepsiptera - Twisted-winged Insects
Siphonaptera - Fleas
This group is referred to as Endopterygota or Holometabola.
Remarks
All the winged insects (including those who have lost their wings over the course of history) constitute the large taxon Pterygota, sometimes treated as a subclass of Insecta.

The sequence of orders of winged insects used in the guide generally follows that used in Arnett (2000)(1). Forum discussions about the sequence of insect orders lead to the consensus (see relevant 2006 and 2007 threads) not to use an alphabetical sequence that would place related groups far apart. Please discuss before making changes.

Pterygota orders listed alphabetically

Further order consolidation is to be expected, as Mantoptera will be lumped with Cockroaches & Termites, and Siphonaptera with what is currently called ‘Mecoptera’.
Internet References
General Entomology by John R. Meyer (excellent source with systematics, descriptions, images)
Insects of Kansas by Roy J. Beckmeyer
Works Cited
1.American Insects: A Handbook of the Insects of America North of Mexico
Ross H. Arnett. 2000. CRC Press.
2.Evolution of the Insects
David Grimaldi and Michael S. Engel. 2005.