By now a lot of people know what the Vex are, parasitic silicon bacteria-like entities that inhabit robotic husks.
So let's start off with the milk. The Vex are microscopic organisms that may be silicon based, which would mean that the Glass Throne is actually thousands of Vex "bacteria" formed into a large structure. They either take this form, circulate through an important structure (like Nessus), or take action in robotic bodies. They work in a hive mind, serving the Collective Mind. Considering that they may be silicon-based, their knowledge and programmings make sense.
As the Vault of Glass gear implies and Asher Mir proves, Vex Radiolaria is extremely parasitic. It's possibly a simple touch of Radiolarian Fluid could start turning you into a Vex Construct. Asher Mir also says that these cells are self-replicating, which is why Taking the Vex is suicidal.
Vex Husks come in many different shapes and sizes. At first glance, they resemble nothing like the Radiolarian Fluid we've seen in their stomachs. Close analysis to one shows wires strewn in their bodies, suggesting the Vex Milk flows through them in order to control them.
The Vex Harpies and Hydras differ greatly from the others in the fact that they are not humanoid. It isn't quite known why the Vex take humanoid shapes most of the time, but what is known is that they still make it work. Many Vex constructs seem over the top, like the Goblins large fan or the Hobgoblins horns. Well, those horns actually make them able to sniper you easier and receive messages faster from other Vex. Hydras are large because they can hold the most data in them. Harpies are mere support units, hence their size.
One of the most interesting things about the Vex is their ability to transform anything into their image. The prime example is Nessus. It isn't quite known how the terraforming begins, perhaps only the mere presence of a Vex construct is all that's needed. Maybe there really is a Vex structure in every celestial body, if so, then Earth can be consumed in days if they activate it.
The Vex can also transform people. Asher Mir's right arm is a Vex arm. According to a description of his status in the grimoire from Age of Triumph, the site where the Vex circuitry meets Human skin is quite grotesque. Asher isn't the only example, however, Kabr also turned into a Vex construct. He drank Radiolarian Fluid, and turned. Also, Guardians who wore the VoG armor sets may have experienced some of the transformation themselves. A Warlock wearing the VoG chestplate woke up to his heart beating to an unknown signal. Possibly the same Guardian recommends to never touch a living Vex, possibly because it accelerates the transformation process. This process is painful, as evidence by stepping in the seas of Nessus.
Vex armor is described as feeling more natural than your own skin, so the Vex clearly nailed comfort. Also, thanks to Asher's arm, we can deduce that a Vex's robotic body is actually made of hardened Radiolarian Fluid. So far, there is no way to reverse the transformation process.
Perhaps the most interesting thing the Vex do is show emotion and devotion. When faced with the Darkness and the Hive and Taken, they turned to either a shard of Darkness or a captured Worm in order to gain strength. We know this as the Black Garden. After seeing us as being superior, they let us clear the Vault, not being able to do it themselves.
Emotionally, the Vex have shown fear towards the Taken. They also feel anger as shown when the Groundskeeper of the Black Garden witnessed his constructs being killed. They also show interest, as Hapax seems to suggest when it goes up and examines Cayde-6 before we kill it. Another example would be their reaction to the crew of the downed Exodus Black.
Their plan is to become a fundamental part of the universe, and we still don't know exactly how they plan to do that.
If I got anything wrong, please comment.
TL:DR - Read it.
Master Post: [url]https://www.bungie.net/en/Forums/Post/234171689[/url]
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So far it's believed that the vex turns things into a vex with contact of this radiolarian fluid. Silica is capable of transferring digital data, we use silica in fiber optic cables. Radiolaria is just like silica, but only this time much more condense and in a fluid form. Planetoids like Nessus are transformed into giant vex by the giant oceans of radiolaria. It's possible this radiolaria seeps through the minerals of the planet and slowly starts consuming it.