No race is more mysterious, bizzare and sometimes - frightening, than the Seeders. The Seeders are the most widely known extradimensional race that currently dwells in our universe, and are responsible for the "Black Planet" phenomena that used to puzzle countless Terran scientists that attempted to study or explain it.
Seeder biotechnology is mind-boggingly difficult to understand, just like the Seeders themselves. In our universe their spaceships manifest themselves as large, swelling, rounded shapes with protruding roots and spikes all over them in complete chaos without a pattern (see attached image). They don't have any uniform types, the largest of these vessels to be ever observed was 500 meters long, although usually they are around half as big. These things resemble and often act similar to strange, exotic plants. They launch swarms of spores that act like missiles/fighters - each one is completely autonomous, and acts not unlike a fighter, but its only means of attack is to ram itself into its target and detonate like a missile. These fighters are not manned.
Even though these ships are very bizzare, unusual and a complete mystery to most, they are not very good at war, and in fact they are pretty easy to obliterate in combat, even for less advanced races.
This fact has caused many agressive races that happened to stumble across the Seeders to underestimate them, and treat them like prey. Any such race payed dearly for that mistake, usually in lives.
Seeders In Combat
The usual scenario was something like this - the alien ship decides to attack the Seeder vessel, fires at a fraction of full power to capture it, and causes significant damage. The Seeder ship returns fire with its spores, causing mild damage that leaves the alien ship almost unscathed. The overconfident alien ship fires all weapons, easily destroying the Seeder vessel. Five seconds later, 50 million Seeder ships appear out of nowhere, fire all at once and easily overwhelm the ship's defenses while the shocked alien crew stares at the sensor screen in disbelief, and dissapear just as abruptly.
The Seeders are well-known both for their ultra-advanced, mind-boggling Maggot-drive and dimensional technologies, and for their capability to draw endless reinforcements, usually engaging enemies with a minimum of 1 to 3 million advantage, that easily compensates the weakness of their ships. Nobody knows where these numbers come from, or in fact, anything much about the Seeders. This race, after all, has come from a far, unexplored dimension.
We do know certain things about them, such as the fact that they are a nomadic species that constantly migrates from one dimension to another, using the Black Plants to store solar energy that will later be used in their jump to the next dimension on their path.
The Seeders are extremely strange extradimentional creatures. A Seeder looks like many hair-width strings, that are divided into rigid sections the ends of which are facing down (most are facing down while some protrude in different directions).
The strings are very long and connect with each other at completely random points that differ from individual to individual, there are hundreds of strings and the whole thing looks like a mess. No organs, central body structure, nothing aside from these weird strings can be seen. They move by using the strings like legs, and by doing so remind the locomotion of insects.
The strings that are their body, dispite being that thin, are extremely tough and thus cut everything that comes into contact with them, like a razor-sharp wire. They will not cut steel, but they can easily cut rock of medium hardness. Also, because they do not have a discernible center of mass, they are difficult to kill. Damaged parts stop moving and become ropelike (lose rigidness) or are detached, but the rest of the body is unaffected, no matter even if its isolated on all sides by dead tissue. It was shown that a body part as small as 5% of the total strings length can live on its own, smaller sections of healthy tissue die off. This mess of rigid strings is something like 7 meters in diameter and 3 meters in height overall. It is colored deep black that can be seen dispite being so thin. Its not very thick, and the spaces left between the strings are large enough to put a human body through. Like mentioned earlier, most of it is facing down, giving it a directed look although some strings create spikes here and there.
If they have politics, we don't know anything about them. We don't know anything about their society, psychology, biology - we are lucky to know what they look like. However, it should be noted that rudimentary communications have been established with the Seeders before, and in fact, a loose friendship exists between the Seeders and the human race. The Seeders have even occasionally intervened in the Human's and their allied races' favour in the wars against the Nec'Toom and their own allies (with varying results). If you'd ask a common human what he thinks about the Seeder race, he would reply that he considers them allies - indeed, in practice the Seeder race is allied with the humans, if not as tightly as some other alien races are.