Haha, you all have such juicy races for me to feast on...

Name of nation: The Hives

Species: L'Er (Eng: One of Us. Note that this is their name for themselves, not one that is used universally by species they encounter. As the nature of such encounters tend to be with feral hives developing on one of their worlds, species often believe the L'Er to be a non-sentient disease at first glance.)
There is no way to accurately describe the entire race, as many, many different forms are constructed. The most common is the small "Spore form". These are arguably the most dangerous form as they possess the ability to bite their way into their host, their organic forms have no skeleton and thus can contort to squeeze through small openings in their host that they cause with their abnormally strong teeth, which are strong enough to bite their way through armour if given a few seconds. Once inside their host, they couple with the hosts central nervous system, making removal almost invariably fatal. It is sometimes argued that they kill the host outright, though there has been no reliable study to confirm this, so it is entirely possible the host is alive and maybe conscious. The host does not have to be alive for this process, a corpse will do. Whatever the case, the Parasite has full control and begins mutating the host. The hive will use the host for a variety of purposes, including but not limited to construction, reproduction and combat. 
This host will now become one of two forms. The first is known as the "Battle" form, this involves the usage of the hosts natural abilities for combat, in addition to mutations to make them stronger, such abnormal muscle growth. This is often done at the expense of the hosts brain and specific organs. Little attempt is made for long term maintenance, as the host will likely be recycled after its purpose is served. The second form is known as the "Transport" form. The is essentially a walking reproductive center for the Parasites, growing new spore forms inside massive bulbous sacks, often mutating the host past what is recognisable. This form shoots the Spore forms out of its many sacks when it sights and approaches an enemy, and has two no way to defend its self except through these spores, although it has been known to fall onto beings which have gotten too close to prevent then from running. Both these forms are called "Impure" forms. There is a third form, though its existence is debated, known as the "Thinker" form. The theory is that certain hosts have their brains kept intact and, in some theories, boosted. These forms supposedly serve as tactical planners in pre-Mind infestations, as well as scientists of sorts or advisors to the mind. Since some intelligent behavior is exhibited in all combat forms, its argued that these are just abnormally intelligent combat forms rather than a new form, though no one is entirely sure.
The next forms are the "Pure forms" These are not mutated hosts but entirely new creatures made out of collected biomass from the planets, including recycled hosts and the bodies of their dead. There are countless different forms which vary from hive to hive. The most important pure form in any hive is the Mind. Without the mind, the parasite has little coordination, and their priority is to begin the construction of a mind. This is not to say they are stupid, they possess the intelligence of their hosts, and though it often degrades over time (with the exception of thinker forms), they are smart enough to coordinate basic tactics (Supposedly thinkers coordinate pre-mind stages) There are three stages (Four if one believes the Thinker Theory)
One: Feral. In this stage, they are uncoordinated and possess limited intelligence. They are still dangerous, but less so compared to later stages. Minor displays of intelligence, such as basic ambushes are known to appear but generally their intelligence is considered to be similar to that of animals at this level. They maintain knowledge their previous hosts had, so the use of vehicles isn't out of the question. They have a weak psychic link which is starting to develop to form the beginnings of a hive
Sapient stage (Thinker theory): According to the Thinker theory, this is the stage where Thinkers begin to show up. They apparently become smart enough to employ advanced tactics, and the weak psychic field between them apparently becomes strengthened to the point it can be used for communication and these thinkers become officers for the fledgling hive. Supposedly these thinkers can be capable of communication with other races, though intelligent communication is often attributed to a later stage, and at this stage it is believed to be simple taunting
Coordination stage: A partially functional Mind has been created. The psychic linked between the organisms has now strengthened to the point that they know each others status at any given time, and they are intelligent enough to communicate with other sentient species in a proper manner, although their previous stages have often resulted in such violence that further conflict is inevitable
Hive stage: The hive has produced a fully functional mind and joined with the other hives of the galaxy. In this stage the Mind has a psychic link with the hive that is so strong that it allows him to speak with others outside the hive across vast distances. The Hive is fully coordinated and can now operate as a proper nation.

Description of government: The government consists of a hierarchy with the Tribunal, a council of three made from the Minds of the most powerful hives, who use their psychic link to communicate with each other and lead the Union of Hives. The major hives come just under them. It has been proposed that there may be some form of "Overmind" by some scholars, but nothing is proven

Description of military: The most common of this species is a small, ball like creatures with small tentacles protruding from it. It uses these tentacles to move, able to climb on surfaces thanks to their suction like design, and to couple with its hosts nervous system and seize control. Their colour varies depending on the hive, and this can be used to quickly identify which hive the Spore forms are from. They have a "beak" of exceptionally strong teeth underneath their tentacles, allowing them to bite they way in, and their lack of a skeleton, small size and relative "squishiness) allows them to fit through small openings they make in their host. They prefer to make such a hole close to the hosts nervous system in order to avoid excessive damage, but forcing their way up appendages is not unheard of. They will then mutate the host or take them to be used. A host can also be mutated if he inhales enough of a gas produced by specially made biomass, however this is a slower process than the spore forms and is less effective. This allows a very flexible army that is able to shrug off most loses in an invasion as they can usually be reabsorbed into the hive or replaced relatively easily

Technological Overview: There is no uniform technology within the hive as they tend to use the technology of their hosts. As such, their weapons range from ballistics to anti-matter. There are a few examples of Hives creating their own technology if the need arises, but given their parasitic nature it is rare. It is known that, once they reach a coordinated stage, they will use any industry they capture to arm themselves. Their space craft range from organic creatures grown around a handful of systems, to entire functional ships that have been merged with and infested by an organic substance which is hostile to intruders, often attacking them where possible. 
As a result of the assimilation dynamic, as well as the ease with which they reproduce, even a small scale infection can quickly become extremely dangerous and large.

Cultural Overview: N/A

History:
 The L'Er date back to evolution on a backwater colony of an interstellar nation. This "Super Parasite" was able to construct a Mind from the biomass of the rampant wild life where it was born. This Mind observed the colonists and their star ships and was able to deduce, after the assimilation of multiple individuals into the hive, that it could sneak aboard Spore forms and infect all the worlds of the species. 
The Mind was able to infiltrate the ships with a small number of spore forms, each of which spread out to the species worlds. At the time, the Mind had little power as it hadn't been further developed, as a result its psychic power was weak enough that the spores that were sent off developed different hives. This separated them into three hives, the original S'Buk, and the successor S'Orp and S'Lif. Out of the three, the original was the most unlucky. The other two worlds of the species were much more developed and larger, and so S'Orp and S'Lif were able to become more powerful than S'Buk as they absorbed more biomass from the worlds and inherited more of the hosts technology, industry and infrastructure.
The Three Hives were able to slowly build up strength and eventually over run the three worlds, absorbing the necessary biomass and leading to the desire to use the host species space travel to find new worlds.
Over millennia, there were several more hives developed across the quadrant and the Union of the Hives was formed in order to advance the L'Er as a whole through inter-hive cooperation. Most of the mentioned new hives are only major to this day with the exception of one, the now Tribunal hive S'Rin. The S'Rin remained the weakest of the hives for many centuries, as they had achieved semi-peaceful relations with the sentients they had encountered and essentially sold themselves as weapons to them. The two species developed under one nation that was budding, and over time the S'Rin were able to gain more and more power, eventually changing from being a living weapon to being an equal partner in the nation. Their hive was weak compared to the others due to their lack of biomass due to having brokered a deal, one which ensured their hives survival but established a blocker to their success however the S'Rin had a plan. They developed a new type of pure form, still used by hives today, called the Worm form. This small form was microscopic and as such it was able to enter the sentients undetected and nestle inside their brain. From their it would secret its toxins to make the individual more susceptible to hive control and eventually place them under the hives control, assimilating them completely. The S'Rin used this on members of the armed forces, slowly bringing control of the military into the hands if the S'Rin. After the S'Rin had secretly gained control of the militaries minds, the organisation that had stopped the S'Rin from assimilating the species before was now on their side. Almost over night the S'Rin seized control using the military and began to assimilated the population into their hive, growing rapidly from a minor power and usurping the place of the S'Buk on the Tribunal now that they had become more powerful than their forefathers. Today, the S'Buk is only a major hive and the S'Rin still hold their place on the Tribunal.
Other hives have been produced since them, and many have come into violent contact with outsiders... And consumed them almost invariably.
Other:
The colour of the biomass varies from hive to hive based on a variety of factors

Below is a government report of known hives, excluding the minor hives which have merely been labelled as "countless" by the writer

Tribunal hives
S'Orp 
S'Lif 
S'Rin 

Major hives:
S'Buk 
S'Kif 
S'Urp 
S'Ein 
S'Ark 
S'Nif

Minor hives: Countless