Insects & other Arthropods David A Kendall   BSc PhD
E-Mail: kendalluk@aol.com
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Classification of Bugs

A guide to the Classes & Orders of insects and other arthropods.
classification

The Insecta (insects) are a Class of the large animal Phylum called ARTHROPODA (arthropods) - a name that refers to the jointed limbs. The other major Classes of living arthropods (i.e. animals related to insects) include the Crustacea (crabs, lobsters, shrimps, barnacles, woodlice, etc.), the Myriapoda (millipedes, centipedes, etc.) and the Arachnida (scorpions, king crabs, spiders, mites, ticks, etc.). In addition there are several minor Classes, the Onychophora (velvet worms), Tardigrada (water bears), Pentastomida (tongue worms) and Pycnogonida (sea spiders), all of which contain somewhat aberrant living forms of uncertain affinities to the any of the preceding groups, and finally a Class of extinct arthropods, the Trilobita (trilobites), known only from their fossil remains. All these animals are characterised by a tough outer body-shell or exoskeleton, with flexible joints between the skeletal plates to allow the animal to move.

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CRUSTACEA MINOR & EXTINCT
CLASSES

Onychophora
Tardigrada
Pentastomida
Pycnogonida
Trilobita
MYRIAPODA
ARACHNIDA
INSECTA

The main external body features which distinguish each of the four major Classes of living arthropods, Crustacea, Myriapoda, Arachnida and Insecta, are shown below (with those that separate the insects from all other groups highlighted in red).

CLASS MAIN BODY REGIONS PAIRS OF LEGS PAIRS OF ANTENNAE WINGS
CRUSTACEA two - cephalothorax* and abdomen (some with head and trunk) five or more two absent
MYRIAPODA two - head and trunk many - one or two per trunk segment one absent
ARACHNIDA two - cephalothorax* and abdomen four none (though palps may resemble antennae or legs) absent
INSECTA three - head, thorax and abdomen three one usually present (but many wingless forms)
*cephalothorax = fused head and thorax

Each of the Classes of arthropods, including the insects, are split into a number of smaller groups, which reflect progressively more detailed structural similarities between the group members. These smaller groups follow a strict hierarchy. The major class divisions in descending order of size are called Subclass, Order, Suborder, Family, Subfamily and Genus. A Genus is the smallest group of any real importance in the naming of individual species, although in some classifications generic groups may be further split into Subgenera. The scientific name of a species includes, first, the Genus to which it belongs and, second, its specific name, e.g. the European Violet Ground Beetle is called Carabus violaceus, meaning the species violaceus in the genus Carabus (by convention, generic and specific names are always printed in italics; the generic name spelt with a capital letter and the specific name with a small letter). The full classification of this insect would be as follows:

PHYLUM:
CLASS:
SUBCLASS:
ORDER:
SUBORDER:
FAMILY:
SUBFAMILY:
GENUS:
SPECIES:
Arthropoda
Insecta
Pterygota
Coleoptera
Adephaga
Carabidae
Carabinae
Carabus
Carabus violaceus L.
arthropod
insect
winged insect
beetle
carnivorous beetle
ground beetle
-
-
violet ground beetle

The name of the author who first describes a species, or a recognised abbreviation of the author's name, is sometimes quoted after the specific name of the animal, in this case L. = Linnaeus (the Swedish naturalist who firmly established the binomial system for naming animals and plants in 1753, and who published the first descriptive account of this particular beetle).

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Class Crustacea

Excluding one or two very small groups of shrimps, the crustaceans are split into 9 main Orders, as listed below. They nearly all live in water and range from minute planktonic shrimp-like creatures, such as water fleas, to the large, more familiar, crabs and lobsters. Some members of the Isopoda are the only forms that have really invaded the land and most of these are largely confined to damp places. Follow the available links for further details.

ORDER COMMON NAME
1. Branchiopoda Water Fleas (Daphnia), Fairy, Brine, Tadpole and Clam Shrimps
2. Copepoda Water Fleas (Cyclops), Fish Lice, Gill Maggots and Anchor Worms
3. Ostracoda Seed Shrimps
4. Cirrepedia Barnacles
5. Stomatopoda Mantis Shrimps
6. Mysidacea Opossum Shrimps
7. Decapoda Shrimps, Prawns, Lobsters, Crayfish and Crabs
8. Amphipoda Freshwater Shrimps (Gammarus) and Sand Hoppers
9. Isopoda Sea Slaters, Water Slaters, Water Lice and Hog Lice
    Isopoda: Oniscoidea (part) Woodlice
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Class Myriapoda

There are four groups of centipede-like creatures known collectively as myriapods. These are listed here as Orders of the Class Myriapoda, but in many arthropod classifications they are given the status of separate Classes.

 
ORDER COMMON NAME
1. Pauropoda -
2. Symphyla -
3. Diplopoda Millipedes
4. Chilopoda Centipedes
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Class Arachnida

The arachnids are usually split into 8 main Orders, as listed below. Follow the available links to see examples of some of these groups.

 
ORDER COMMON NAME
1. Xiphosura King Crabs or Horseshoe Crabs
2. Pseudoscorpiones (= Chernetidea) Pseudoscorpions or False Scorpions
3. Scorpionidea Scorpions
4. Pedipalpi Whip Scorpions
5. Solifuga (= Solpugae) Wind Scorpions or Barrel Spiders
6. Opiliones (= Phalangidea) Harvestmen or Harvest Spiders
7. Acari (= Acarina) Mites and Ticks
8. Araneae True Spiders
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Class Insecta

The insects are generally sub-divided into 29 Orders. These are listed below with links to pages describing general characteristics, recognition features and examples of each Order. You can also follow the link at the bottom of this page for a simply identification key to most of these Orders.

 
ORDER COMMON NAME SUBCLASSES & FEATURES
1. Thysanura Bristletails
APTERYGOTA

These are wingless insects and their body structure suggests that they have never had wings during their evolutionary history. Young stages resemble the adults - little or no metamorphosis.

2. Diplura Two-pronged Bristletails
3. Protura -
4. Collembola Springtails
5. Ephemeroptera Mayflies
PTERYGOTA
Division EXOPTERYGOTA

These are winged insects, although some have lost their wings during the course of evolution.When present, the wings develop externally and there is no marked change (metamorphosis) during the life cycle. The young stages, called nymphs, resemble the adults except in size and in lacking fully-developed wings - simply metamorphosis.

6. Odonata Dragonflies
7. Plecoptera Stoneflies
8. Grylloblattodea -
9. Orthoptera Crickets, Grasshoppers and Locusts
10. Phasmida Stick and Leaf Insects
11. Dermaptera Earwigs
12. Embioptera Web-spinners
13. Dictyoptera Cockroaches and Mantids
14. Isoptera Termites
15. Zoraptera -
16. Psocoptera Psocids or Booklice
17. Mallophaga Biting Lice
18. Siphunculata (= Anoplura) Sucking Lice
19. Hemiptera True Bugs
20. Thysanoptera Thrips
21. Neuroptera Alder Flies, Snake Flies and Lacewings
PTERYGOTA
Division ENDOPTERYGOTA

These are winged insects, although some have lost their wings during the course of evolution. When present, the wings develop internally (i.e. inside the body of the immature insect) and there is a marked change (metamorphosis) during the life cycle. The young stages are very different from the adults and are called larvae. The change from larva to adult takes place during a non-feeding stage called the pupa (or chrysalis) - complex metamorphosis.

22. Coleoptera Beetles
23. Strepsiptera Stylopids
24. Mecoptera Scorpion Flies
25. Siphonaptera Fleas
26. Diptera True Flies
27. Lepidoptera Butterflies and Moths
28. Trichoptera Caddis Flies
29. Hymenoptera Bees, Wasps and Ants

The first priority when trying to identify an unknown insect is to determine its correct Order. This can be done for many common insects with the aid of a hand-lens and a moderately simple key.

KEY
(click icon for the identification key to insect orders)

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Copyright © 2010 David Kendall Last revised May 2010