Yatevians

Yatevians are the first alien species ever encountered by Mankind. Their extremely alien physiology and mentality were a good introduction to the long (and painful) history of human contacts with other xenospecies. They are counted among those aliens that cannot be reasoned with - in fact, they are alien enough that xenopsychologists to this day aren't sure if they possess sapience. All that the yatevians know is relentless hunger - and they can are ready to do anything imaginable to satiate it.
This, together with the fact that they somewhat resemble plants, has led to them receiving a number of names resembling to a maneating plants. 'Yatevian' name hails from yateveo, a fictional maneating trees supposedly native to Africa and Central America, described in J.W. Buel's book Sea and Land in year 1887. They are also called triffids, after another, much more popular writing.
One of the theories about the nature of yatevians is that they are a self-replicating bioweapon that long ago freed itself from its restrains. Nobody knows how many alien civilizations fell to the relentless hunger of this xenospecies - because nobody how far they spread. Everything that Mankind knows about them is the unbreakable wall of murderous aliens that encompasses majority of its 'western' border and seems to be too deep to traverse.
Confederation of Mankind achieved some regional successes since the First Contact War, pushing the border back slightly. However, there could as well be hundreds of thousands of yatevian-held worlds as well as quadrillions of those killing machines left. What's worse, it is believed that the yatevians are steadily closing the technological gap between them and Mankind...

Basic Information

Anatomy

Attempt to classify yatevians according to Earth' classification is downright impossible. They are alien in every sense of the word. Their biology incorporates elements of fungi, plants and animals in one, cohesive form.

Plants true form is a fungi capable of transforming silicon into neural systems, composed of soft mycelium cerebral cortex analogue, hard silicon core and wood-like shell, with many protruding nerve bundles.
Through the nerve bundles, plants connect with many species of plants analogues from their homeworld, that during long evolutionary process were made dependant of the parasitic fungi (which plants de facto are), that is capable of taking over their nervous system. They are also capable of modyfing the parasitized organisms by using enzymes they are naturally able to produce to modyfy their DNA code.
Most of the Plants natural form is massive (up to five meters length, three height and three width) quadruped composed of plant-like matter. That is surprisingly fast and strong, not to mention that it can only be killed by shaterring the core that is safely hidden beneath plant matter and thick shell.

Ecology and Habitats

They take their own ecosystem (one capable of reproducing fast enough to sustain them) with them, replacing the encountered ecosystems with their own. Thus changing every planet they colonize into a world of ultraviolent jungle-analogue, filled with agressive flora and fauna that they can hunt and devour.

Dietary Needs and Habits

They are an agressive specie of omnivores, that are sustain both through food intake and photosynthesis. They never truly learned agriculture, remaining on the paleolithic level of being hunter-gatherers.

Additional Information

Average Intelligence

The scientists are still unsure if the Plants are actually sapient in human terms. This is caused by their absolute memory. Plants remember literally every single second of their life. And every detail - literally every sensory input, from eyesight to touch - of it.
Their ability to construct space ships might be caused by their contact with Lights, with all (or nearly all) further progress connected to Plants observing other races or dismantling their capture equipment.
While relatively dumb by human standard, they possess insane learning capability. Plant faced with something unknown will have great problems with figuring out what he is facing, however after achieving this once he will never forget this and next time he will react properly immediately. This is the cause of their extreme combat prowess, with Plants remembering exactly every tactics and weaponry used against them. Other races were force to adapt KILL THEM ALL strategy against them, since letting even a minuscule part of their forces flee meant facing it again, much stronger and wiser.

Perception and Sensory Capabilities

They feel touch with microscopic hairs covering thier photosyntetic equivalent of skin. Their eyes are primitive and insect-like. They don't have eyeballs, instead they evolved receptors visually similar to faceted eyes on small antennae. Dome-like shape grants them 120 degrees of clear field of vision (for reffrence humans are 120 times worse at it). They have very basic hearing (evolved only after thier "contact" with Lights). Voice appeared only after the First Contact War ans is also rather basic, exceptions are those plants who assimilated into human society.

Civilization and Culture

Average Technological Level

Space War

In space Plants are really, really weak, despite the fact that they had 250 years to catch up to humanity and other races. Their biggest problem is that their neighbours develop new technologies, faster that they can steal them. And most archeotechs can't be dissambled and reassembled while learning how to mass prodce them. Their impact on technological progress is achieved by longterm analysis and attempts to fir them in existing theoretical science. Plants are completely incapable of that.
Thus Plants are force to rely on stealing technologies from their neighbours. Here, however, they meet another problems. Most of the space races they neighbour with is simply too advanced. Plants lack technology required to understand and use what they steal.
There is still a notable improvement though. Today the Outer Colonies warships of similar tonnage are only approximately three times as strong. During the First Contact War, the difference was nearly seven times bigger.
Their ships are very varied in forms. Most of them is based on their neighbours ships that somehow appealed useful to Plants shipyard workers. Their biggest advantage is the fact that they are made more organic. The inside of every such ship is basically a Plant, very old and very big. Vacuum is deadly for it, but the death may take weaks if they cut all sensory input from the parts of its body that were exposed to it. Their regenerative abilities border on magic, which means that Plants ship can easily repair internal damage.
Side effects? Their hulls are fragile, and ever hit means more damage that it should. On the other hand, if the ship isn't destroyed completely and it's Plant (working as a organic computer of sort) killed, the Plants WILL manage to repair it. And it's core Plant will remember how exactly it got damaged for future reference.

Ground War

On ground Plants are utterly terrifying menace despite their primitive technology. There are always plenty of them and they are very resistant to enemy fire. Small calibre rounds are practically useless, not to mention melee weaponry (with their strenght and speed they are almost always capable of disarming the oponent and decapitating him with his own weapon). The only things capable of defeating a Plant warrior is large-calibre weaponry (that is average at best, since it must hit the core that can be everywhere) or heavy weapons.
In fact, a grown and experienced Plant warrior armed with their weapon of choice - heavy firearm mounted on their backs, with calibre equaling smaller human cannons and a dozen or two fo antitank magnetic mines - is equall in strenght with average human tank or mecha. Over which they prevail in mobility, reaction speed and numbers. Since sometimes they equal the oponent infantry in that last department.

History

Humble Beginnings

The true origin of the yatevians is unknown - which shouldn't be surprising. Nobody knows where their homeworld is. And even if it was known, then reaching it would require fighting your way through untold number of sophisticated biological killing machines. What's worst, it doesn't even have to be in one of the sectors reachable by hyperlanes. With yatevians themselves possessing no way of storing information (nor anything even remotely resembling culture), there is literally nothing to left to base theories on save for pure speculations.
At present, there are two theories. First is the natural evolution theory, while the other is an engineered being theory.
Natural Evolution Theory is based on an extreme form of a survival of the fittest. Proponents of this theory suggest that yatevians evolved on what can only be summed up as an extremely sophisticated death world. They became the dominant species with their ability to learn and propagate this knowledge throughout their species. Every discovery must have took them an untold centuries of completely random events, but once made, it spread without a fail.
Either that continued ad infinitum, or some unfortunate second species landed on yatevians' homeworld, ending up devoured and with their technology expanding the natives knowledge. Whatever option was true, they ended up spreading throughout the stars.
Engineered Being Theory claims that there was no homeworld. Yatevians were instead developed as a biological weapon. Self-replicating killing machines dedicated to utter annihilation of all forms of life, not unlike the Berserks. Or, due to their organic nature, the ancestors of Shoggoths. Either they ended up annihilating creators, or where unleashed after they were wiped out by something... or said creators are still around.
This ended up with them spreading out throughout the stars.

Relentless Spread

Yatevians began spreading throughout the stars - and failed to stop. They do not really possess ability to formulate longterm plans. They keep reproducing, until their worlds cannot contain them - and they the surplus population departs towards the stars, seeking more food. Most of such fleets die out before finding a good world. The rest settles new worlds, spreading their known plant and animal life that quickly devours everything that used to live on them. However, those colonies eventually became overpopulated as well. This makes them send even more migration fleets... and so it goes, ad infinitum.
The yatevians possess no ability to terraform worlds, which makes them able to colonize only relatively insignificant amount of worlds. However, they do not think the same way as other species. They spread throughout the Galaxy ignoring the hyperlanes (they didn't even know how to use them until the First Contact War). During their war with Mankind only their worlds near the hyperlanes contributed to the war efforts. The rest is in most cases yet to learn of humanity existence. It is quite possible that their are currently waging wars against dozens of other species on their other borders (probably annihilating and devouring them all, one by one).

First Contact War

The exact details of the very beginning of the First Contact War are shrouded in mystery. Those responsible for the actual first contact didn't survive to tell the tale. What is known for sure is that in year 2310 an armies and fleets of those sophisticated killing machines suddenly invaded Human Space. The initial shock was so great that it made the Solar Federation (under the rule of the Reconciliarists) and the Confederation of Mankind ally with each other and wage total war against the new outside threat.
The battles in space were an absolute massacre, as yatevians required to possess at least twenty times the tonnage of their enemies to have a chance in winning. However, this actually happened quite often - mostly because of the absolute lack of self-preservation instincts of the yatevians. Annihilation of their opponents is an absolutely overriding instinct, something that they really can't help. They launched themselves at human fleets without restraint, often overwhelming them with nothing but their numbers.
On the ground the battles were massacres as well... but humans were on a receiving end. Yatevians didn't care about the distinction between civilians and combatants. They also possessed numbers equaling those in space, but with the technological edge of the humans being less sharp. In fact, the aliens mostly made up for it with their superhuman physique. Because of that several planets were lost (their inhabitants mostly devoured) and due to spread of yatevian-derived lifeforms had to be cauterized after being retaken.
Ultimately Mankind has triumphed, with yatevians suffering from such a casualties that they could no longer maintain their relentless assault. But there is no peace - they simply started sending smaller fleets in response to overpopulation on their worlds. What's more, their technological basis began improving with rather fast pace. Nobody knows why that happens, as it is believed that prior to the First Contact War the yatevians were technologically stagnant, relying on their numbers to defeat their opponents.

Lifespan

Infinite

Average Height

3m

Average Weight

1,5t

Average Length

5m