Ptera-squirrels are a species of mammal that seem to infest the planets, ships, naval stations... pretty much everywhere that the Imperium of Man controls. It is a rodent-like species the size and morphology similar to ancient Terran flying squirrels, only with slightly longer arms and fangs. Their flaps between their arms and legs allow them to glide across long areas, which gives them an important mobility advantage, on top of the natural agility they have from being squirrels.
Ptera-squirrels are scavengers by nature. Eating whatever they can get their paws on, they are quite the opportunists, munching on anything that might feed them. Like the rodents of old, the ptera-squirrels reproduce like crazy, having numerous offspring in relatively short breeding cycles, and this and their ability to sneak around in human ships makes them quite able to infest their living spaces in no time. As such, they seem to be a prime candidate to drive other species away once they reach a new planet. While Ptera-squirrels seem to be relatively peaceful creatures most of the time,once in a while ptera-squirrels will give birth a generation much more aggressive than the ones before. They will crave for blood, and will attack anyone and anything that might have it, like some form of vampire squirrels. These sudden periods are incredibly dangerous for those spaces affected, especially closed spaces such as the cargo bay of a ship, where they can use their small size, numbers and blood-thirst to wreak havoc upon the workers there. And, just as fast as it came, that rage will disappear and the ptera-squirrels will go back to their seemingly peaceful ways.
As you can imagine, this makes the ptera-squirrels to be considered as pests to be eradicated, though considering the amount of danger the galaxy has on a regular basis, dealing with these rodents is probably quite easy.
Relationship with MankindEdit
Humanity is probably guilty of spreading this species throughout the stars, and as such, they have coexisted for many millennia. While the sight of ptera-squirrels in hive cities and ships is not a particularly rare sight, there is no real urgency to deal with them. They are to be attacked and driven away on sight, yes, but there are much, MUCH more dangerous pests throughout the Imperium, so they don't get that much attention outside of local authorities. Besides, humanity has probably developed quite a lot of ways to deal with them, just like they developed tools and protocols to stop rat infestations. Agriworlds might be much more prepared to deal with this pests due to the risk of them damaging their produce because of this, though the small size of the squirrels makes it very difficult to actually eradicate from open spaces.
Also, just as the ptera-squirrels can be seen attacking humans and feeding on their carcasses while available, it is not rare to see humans hunting down the rodents for their meat.
How they came to beEdit
Most studies seem to agree that the Ptera-squirrel came from Terra, due to the previously mentioned similarities with the ancient flying squirrel. This would seem like a sensible option due to that species being quite adaptable and, with enough natural selection, evolve quickly into the ptera-squirrel. However, it cannot be confirmed due to the lack of genetic comparison and almost nonexistent records. Another possibility is genetic engineering, though what would be the point of that project is, again, a mystery.
There's also the possibility of slow mutations due to the influence of the Warp. Considering it has coexisted with Mankind for millenia, and one of its preferred modes of spreading is through human ships, warp capable ships, maybe they've been slowly altered by the mutating effects of the Warp through hundreds of thousands of generations. That would explain the random blood-thirst this species enters in once in a while.