The Swarm

History
For as long as humans have been in this sector, there has been an ever present danger form the north. Named the swarm by early explores for the way there seamed to be an exhaustible number of them, packed together ravaging anything in their path.

During the time of the Mandate, they were not very active, mainly raiding outlying outposts all arose the northern half of the sector. However in recent years they have increased their assaults and begun focusing them on a handful of planets.

Physiology
There are many different versions of creatures that make up the swarm. But they can be sorted in to classes based upon what there purpose is. In general creatures of the swarm will have a insect like temperance, with multiple extra limbs, and a chitinous exoskeleton.

Class 1
These type largest and most alien of all the swarm. Called hives, these are the closest things the swarm have to buildings, but they are not, as they can move and are intelligent. They come in many shapes and sizes, but they all serve the same purpose, to grow other swarm creatures. They are most like our factories, taking in raw matter and outputting swarm creatures of all types. They can range form the size of a room, to make the smallest swarm creatures, to as large as a station, when they make the star fairing type.

An interesting note, Hives can create things slightly bigger then themselves, allowing a chain of larger and larger hives to create a larger verity of creatures.

Class 2
Theses unique creatures, from the backbone of the interstellar travel of the Swarm. They are able to integrate themselves with small to medium inorganic space junk, and provide it with the ability to make powerful spike drills. The current theory is that they are powerful psychics, with sole focus on manipulating meta dimensional space (not dissimilar form a teleportation specialist, but much more powerful and specialized)

Once the creature is bound to its host (general a small comment) it is complacently dependent, and is never able to unbind itself.

Class 3
These are the organic space crafts that the swarm use when attacking a system, created out of the hives they are the swarms equivalent of star ships, however there has never been seen a interaction between class 2s and class 3s, so it is safe to assume that none of these "ships" have a spike drive.

Class 4
The largest class of creatures, and also the most numerous. This group is representative of all the ground forces that the swarm grow. "vehicles" and infantry equivalents are all in this class

Class 5
The simplest class, this is the "workers" or drones. They do the mealiness tasks such as transforming locations, digging tunnels or creating new comments for interstellar travel.

Common attack pattern
The common pattern for the swarm in the modern age is to first send an comet loaded with several hives, and a host of small class 4 creatures, to a location they want to attack, generally an outer moon or small planet. They there establish a well protected hive core, general underground.

The next step is to expand outward with bigger and bigger hives and forces until the entire world is under their control. The whole while Class 3s are being made, along with large bio-transports that will allow massive invasion of other worlds.

The best way to stop an incursion is to destroy the comet before it touches down, because once it has, it takes a large force to clear base, so long as all hives are destroyed, no new ones can be created and the incursion will eventually die out.