The underlying principle of taxonomy is that animals that have a common ancestry and share features are grouped together.
The 17th century naturalist John Ray introduced the concept of a "species", and since then this has been the basic unit of classification. There are seven mandatory groupings (taxa) from kingdom to species, these are; kingdom, phylum (plural - phyla), class, order, family, genus, species. So the buff-tailed bumblebee is:
It is possible to further subdivide these taxa by the addition of the prefixes super-, sub-, and infra, to give over 30 taxa. This enables the degree of divergence of large, complex groups such as the Hexapoda to be expressed.
Quite often just the genus and species are used when referring to an animal; this is the binomial system introduced by Carl Linnaeus in the 1753. Both genus and species should be printed in italics or underlined when written, and the initial letter of the genus should be capitalised, e.g. Bombus lapidarius. After the genus and species there may be a name and date in brackets, this is the name of the person who first described the species and the date of the published description. It is this first "type specimen" description that is used to identify all other individuals of the species.
The reason for all this is quite simple - it enables world-wide communication. Forficula auricularia can be understood by scientists in any country of the world, regardless of their mother tongue, the two common names I know for this animal are "earwig" and "forkytail". However I have no idea how to say this in French, for example, and even if I could find the word in a dictionary, I have no idea if the French translation refers to Forficula auricularia, or to another species in the Forficula genus. so, when it come to naming animals and plants Latin and Greek are still the international languages! To see just how confusing common names can get visit the FAQ page on the bumblebee.org site.
Another function of a scientific name is to reflect the relationships between organisms. For example you can tell if animals have the same genus name then they must be closely related, e.g. Bombus terrestris and Bombus hortorum. Also that Bombus terrestris is more closely related to other bees in the Bombus genus than to Apis mellifera (the honey bee), which is in the same Family, Apidae as Bombus terrestris.
An organism's taxonomic position is not static, and can be changed as further discoveries are made. There are also differing schools of thought as to the placing of individual organisms and higher taxa, therefore there WILL be differences between textbooks. For example the Phyla Chelicerata, Uniramia and Crustacea are often grouped into one phylum the word "Arthropoda"; on this site they are kept separate, and Arthropod is used to refer to all animals with jointed legs.
It must be stressed that there is no single "correct" classification. This is not terribly important, unless you become a taxonomist; the important thing is to try to note the characteristics that make one group different or similar to another. It is also possible for a species unwittingly to be given two or more names, this is rectified as soon as possible, and the earlier name usually has precedence.
Spelling and pronunciation of the Latin names usually cause those without a classical education, and nowadays that's most of us, some difficulty. There is no easy way to overcome the spelling, but you are unlikely to lose marks in exams or in class if the mistake is slight and the word is recognisable. For essays and reports the spelling should be checked at all times as you will have access to books and the internet on these occasions. Pronunciation is easily overcome, "say it loudly and with confidence, and few will have the nerve to correct you", was the advice given to me by one lecturer, and it has worked so far.
Throughout this site numbers of living or extinct species of different phyla or classes will be given. It must be stressed that these are the number of known, described and named species; the true number of species will be much higher. There are a number of reasons for this. New fossil evidence is being found all the time, and this adds to the number of extinct species. Every day new invertebrate species are found, this is especially so with the insects, and in particular the beetles, flies and parasitic wasps.
There are not enough taxonomists available to keep up with the new discoveries so it takes time before something is officially described and named. Estimates for the true number of insects can reach as high as eighty million; only about a million of these have so far been named. Extinction is a natural process but we appear to be going through a period of relatively rapid extinctions; mainly linked to anthropogenic changes in the environment. So, sadly, there will be species going extinct before they have even been discovered.
80% of insect taxonomists are in North America and Europe. Taxonomists are an endangered species! Most of the IUCN's red list of threatened species is limited to vertebrates and higher plants. This is because to declare a species as threatened you need data - data from the past to show what we had, and data from the present to show what we've lost.
For most invertebrates not only do we not have past and present data, we usually haven't even formally described the species. Many are gone before we even knew we had them, never mind their abundance, range, ecology and behaviour.
So if you have money to spare, fund taxonomy. Museums throughout the world have drawers and boxes full of specimens that need formal identification, and they lack both the staff and the money to do so. You can help, and they may even name a species after you, so your name will live on long after you have gone. I have a special fondness for dung beetles; their habits are obnoxious to humans, but without them we'd be knee deep in the stuff they call home. I can never forget the first time I saw one close up, it was lying on its back on my hand and as it unrolled itself I caught a glimpse of long, shiny ginger hair on a steely-blue abdomen with an iridescent sheen. I can honestly say I have never seen anything more beautiful in my entire life. If I am ever rich I will try to have a dung beetle or something similar named after my dog, who is the second most beautiful thing I know.
Over 98% of the Kingdom Animalia are invertebrates, and of the invertebrates around 80% are insects. So we live in a world of beetles, flies and parasitic wasps! Just think about this. If an alien spacecraft visited the Earth today to sample species of terrestrial life they would most likely go back home and describe Earth as a planet of six-legged vegetarian animals usually 3 - 40 mm in length!