Perhaps the most off-putting things about entomology is that none of the things have common (vernacular) names.  Hopefully this will clear some of the confusion.

First, why bother with scientific names (preferred to Latin names as many are Greek) at all?  Whenever a new species is found, it is assigned a scientific name.  This uniquely identifies the organism and is universal throughout the world.  There is no need to introduce a vernacular name.  Also, the Hogweed Bonking Beetle and Swollen-thighed Swollen-thigh (genuine suggestions) may not be understood even in the country of origin, let alone internationally.

Each name is fully described by four parts: The genus name, the species name, the author and the date.  An example would be Dytiscus marginalis Linnaeus 1758.  By convention, the genus and species names are in italic script.  The genus is capitalised while the species name is lower-case. The species name must agree in gender with the genus name hence the change from Delichon urbica to Delichon urbicum as the House Martin.  The original was a relict from Linnaeus’ original classification where urbica agreed in gender with Hirundo.

The genus name must be unique within a Kingdom (Plant, Animal, Bacteria, Fungi and Protist).  However, they do not need to be unique across Kingdoms.  Thus Oenanthe is the Wheatear in the Animalia but Water Dropwort in the Plantae.

Then comes the rules on naming.  This deals with changes in genera, two people describing the same species and people giving two species the same name.  Most of this occurred as a result of the rush to name European fauna in the late 1700s and early 1800s.  These are adjudicated by the International Convention on Zoological Nomenclature.

Poecilus cupreus (Linnaeus) 1758.  Linnaeus placed this species in the genus Pterostichus.  The author name is placed in brackets to denote a change in genera.

If two authors described the same species, the first name chronologically takes precedence.  This is called the Principle of Priority.  Hence Dysticus semisulcatus Muller 1776 takes precedence over Dysticus punctulatus Fabricius 1777.  There are approximately 2 -3 million of these.  This means mistakes are very difficult to correct.  Hence Apis mellifera Linnaeus 1758 takes precedence over the more scientifically correct Apis mellifica Linnaeus 1761.  Likewise Aeshna isoceles Muller 1767 was a spelling error and various groups are now striving to get the name changed to Aeshna isosceles.

Sometimes two authors used the same name for different species.  This is best illustrated using the weevil Curculio fasciatus Scopoli 1763.  Scopoli described a species from Slovenia.  The following  also described a Curculio fasciatus: Strom 1768 (Norway), De Geer 1765 (Sweden), Muller 1776 (Denmark), Fourcroy 1785 (France), Olivier 1790 (France) and Marsham 1802 (Britain).  In this case we use non, nec or not between the primary author and subsequent authors: Conus catenatus Sowerby 1850 nec Sowerby 1875.

Sometimes the above rule does not apply.  The Commission has ruled on 17 species where the wild form is pre-dated by its domestic form.  For this reason, the Domestic Cat Felis catus Linnaeus 1758 should take priority over Felis sylvestris von Schreber 1775.  However, the Commission has ruled that F. sylvestris shall be conserved.  For those who believe the two to be the same species then F. sylvestris should be used, for those who consider them separate speceis F. catus and F. sylvestris are used and those that consider the Domestic Cat a subspecies should use F. sylvestris catus.

Sorry it was a bit heavy on science and words with no pretty pictures.