// Just a forewarning, sex with Tyranids will be violent rape for the most part //
The Tyranids are an extragalactic composite species of hideous, insectoid xenos. They actually comprise an entire space-faring ecosystem comprised of innumerable different bioforms which are all variations on the same genetic theme.
The Tyranids are unlike any other intelligent species encountered by Humanity. They are the ultimate predators; to them, all living things, from the lowliest insect to the most advanced starfaring civilisation, are mere prey. Only now are the inhabitants of the galaxy realising the scale of the threat; unless the Tyranids can be stopped, it will mean nothing less than the extinction of all life.
The Tyranid species is ultimately dedicated solely to its own survival, propagation and evolutionary advancement. The Tyranids collectively form a monstrous superorganism that travels across the universe in their great hive fleets of biomechanical Hive Ships, systematically consuming all other biomatter to enable their own rapid evolution and reproduction.
The Tyranids are likened to a galactic swarm consuming everything in its path, feeding on entire worlds and leaving only dead husks in their wake. Their threat is such that an unprotected planet can be infested and stripped clean of all its organic material in a matter of solar weeks without even slowing down the advance of the hive fleet.
All Tyranid organisms are "synaptic" (psychically-reactive), and each Tyranid creature within a hive fleet shares and contributes to a communal Hive Mind, which allows the trillions of beings comprising the Tyranid hive fleets to communicate and organise instantaneously on a staggering scale.
The mentality of the Tyranid approach to warfare can be described with the phrase "quantity has a quality all its own." From the "lowly" Ripper, to the deadly Hive Tyrant and beyond, the signature of the Tyranid species is that they overwhelm their foes with sheer numbers, reproducing massive numbers of highly virulent organisms in record time from the biochemical soup that they derive from the biospheres of the worlds they consume.