The GuildWiki Bestiary Index
The goal of the GuildWiki Bestiary Index is to collect as much information as possible on all of the various creatures one might face in the game, and organize them by species and in some cases political affiliations too.
To see the current state of the Bestiary take a look at Category:Bestiary.
In Guild Wars, a species (or "type of creature") is a group of creature types that usually share a similar look, similar behaviour and often a part of their name, for example Carrion Devourers and Whiptail Devourers both belong to the species Devourer. One exception is animal companions, where Black Widows, Striders, Warthogs, and other different charmable animals are considered "creatures of the same type".
Creatures of the same species usually drop the same crafting materials and similar trophies and salvage items. For example Devourers all drop Chitin Fragments as material and "Carapaces" of some kind.
Sometimes certain professions are predominant among a species, for example Devourers are mostly Rangers and Necromancers. This is true of the less developed species and monsters. For more developed species, however, (like Charr or Centaur) they tend to cover the full gamut of professions.
Certain weapon upgrades "of <species>-slaying" provide bonuses when fighting against all creatures of the species, for example a "Sword Pommel of Dwarfslaying" will provide increased damage and/or armor against Dwarves.
 Political affiliations
Political affiliations may be guilds, nations, clans, or merely individuals banded together for a common cause. Some of the more martial affiliations wear emblems or badges to mark themselves, which can appear as trophies. Their ranks tend to run the full gamut of professions.
Political affiliations need not be consisted of creatures of the same species. Different species may willingly band together, be enslaved by one another, or be created to act as servants of another.
Examples of this are: