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The branch of science primarily focused on classifying living organisms is known as taxonomy. Differences between taxonomists worldwide can result in different classification systems. That’s why names and references may differ from the classification system used in Australia. 

Generally speaking, living organisms are classified according to seven primary levels:

1. Kingdom
2. Phylum
3. Class
4. Order
5. Suborder
6. Family
7. Genus
8. Species

For the purpose of the providing a brief overview of classification, living organisms can be classified to one of the following  kingdoms:

Monera – bacteria

Protista – algae, protozoans, slime moulds

Fungi – fungi, moulds

Plantae – non-flowering and flowering plants

Animalia – animals

Each animal belongs to a phylum, which is the next level down. Animals can be divided into vertebrate or invertebrate, but they can be classified further. For example:

Phylum Porifera – sponges

Phylum Coelenterate – jellyfish, corals

Phylum Platyhelminthes – flatworms 

Phylum Annelida – roundworms, earthworms

Phylum Mollusca – snails, slugs, clams, oysters, and other mollusks

Phylum Arthropoda – insects, spiders, mites, etc. 

Phylum Chordata – back-boned animals (mammals, reptiles, birds)

Although there are many animals that invade our buildings from the Phylum Chordata (rats, mice, birds, possums), the most prolific and successful pests we encounter are from Phylum Arthropoda. 

Some characteristics that members of Phylum Arthropoda share include:

1. Segmented bodies that are arranged in regions called tagmata (e.g. head, thorax, and abdomen)
2. Paired appendages
3. They possess chitinous exoskeleton that must be shed during growth
4. Bilateral symmetry
5. The open circulatory system located ventrally and the nervous system is located dorsally

Each phylum is further divided into several classes, each of which represents a group of animals. These animals not only exhibit the basic traits of the phylum but also share specific additional characteristics. The characteristics used to differentiate between arthropod classes mainly involve morphological features such as the number of body segments, the number of paired legs, and the presence or absence of antennae. 

For example:

• Class Diplopoda (millipedes)
  • The body has many segments that are rounded and each segment has two pairs of legs
  • Antennae are present
• Class Chilopoda (centipedes)
  • The body has many segments that are dorsally flattened and each have a pair of legs
  • Antennae are present
• Class Arachnida (spiders and mites)
  • Members mostly have two body segments 
  • Four pairs of legs
  • Antennae are absent
• Class Insects (insects)
  • Three body segments
  • Three pairs of legs attached to the second body segment (thorax)
  • Antennae are present 

There are over one million described species of insects, and they all been organised and classified within class by dividing them into a number of insect orders, each of which contains class members that have certain morphological features in common. For example, insects that only have two wings are called “true flies”, and they belong to the order Diptera (di = two, ptera = wings).

Each order is then broken up into a number of families, again based on morphological features. For example, under order Diptera, there are almost 90 families. Mosquitoes belong to the Family Culicidae, hover flies belong to Familt Syriphidae, and drain flies belong to Family Psychodidae. Further morphological characteristic divide each family into a number of genera (singular:genus), and the members of each genus have much in common. Each genus then contains one or a number of species, and a species represents a group of individuals that share common characteristics that are capable of inbreeding. 

Finally, there are observable morhpological differences between males and females of the same species – this is called sexual dimorphism. For instance male and female houseflies have different distances between their eyes; females have a wider space between their eyes than males. Another example is male mosquitoes have additional plumage on their antennae compared to female mosquitoes. 

The broad classification of some familiar animals

Classification grouping	German Cockroach	American cockroach	Red Imported Fire ant	Norway rat	Humans
Kingdom	Animalia	Animalia	Animalia	Animalia	Animalia
Phylum	Arthropoda	Arthropoda	Arthropoda	Chordata	Chordata
Class	Insecta	Insecta	Insecta	Mammalia	Mammalia
Order	Blattodea	Blattodea	Hymenoptera	Rodentia	Primates
Family	Blattillidae	Blattidae	Formicidae	Muridea	Hominidae
Genus	Blatella	Periplaneta	Solenopsis	Rattus	Homo
Species	germanica	americana	invicta	norvegicus	sapiens
Scientific name	Blatella germanica	Periplaneta americana	Solenopsisinvicta	Rattus norvegicus	Homo sapiens

Naming Animals

All organisms that have been described and published were given a scientific name. Some organisms also have a common name. However, unlike the the scientific name, common names may vary from country to country, or even within a country. THere are some rules for reading, writing, and understanding scientific names. For example:

Common name: Housefly

Scientific name: Musca domestica Linnaeus

1. Musca – This is the name of the genus which the housefly belongs. Scientific names are always italicized, and the generic name starts with a capital letter.

2. domestica – this is the species name which the housefly belongs to. The specific name always starts with a lower-case letter. It is important to remember that you cannot use the specific name on its own as it would not mean much because there are many animals that have the same specific name. For example, the specific name norvegicus may refer to Calocoris norvegicus, a potato bug, or Rattus norvegicus, the Norway rat.

3. Linnaeus – This is the name of the scientist who originally described and named the fly. If the name appears in brackets, changes to the name of the species have been made following the original description. The author’s name is not usually included in texts (or inspection reports), but it can be useful to taxonomists. 

The Major Insect Orders