It was a huge battle, they ended up having to ACTUALLY call for help in the form of human space marines. Why? Because these unknown creatures that had attacked the colonial world had been so powerful that the Vorax ships it'd passed had turned tail and fled as fast as it could, after seeing how easily it had overcome two of their biggest warships.
The humans actually were having a challenge with this battle, not just in space but on the ground. These monstrous beings were insect-like in form, very highly intelligent, and had a 'take no prisoners' philosophy. It wanted this world for its own, to strip it bare of resources as it had done other worlds this species had encountered, before it inevitably moved on to other worlds.
One human, to encourage his men, pulled out the one song that had become their battle-cry. And as it blasted over the loudspeakers, it reminded others again, just why so few wanted to face a Space Marine on the field.
(this is the song, along with the lyrics)
https://www.youtube.com/watch?v=jFi7bWkyRpA -- Anon Guest
The moral of the ocean is, there is always a bigger fish. The same can be plausible for space. There is always a bigger Deathworlder. Everyone knows of the Vorax. They were once the most deadly Deathworlders for centuries. Then there was the unnamed swarm that never had their own name.
Humans called them Those Bastards. They would get no other name. They were so voracious and aggressive that even the Vorax kept their distance, and the Vorax were famous for retreating only from one other species - the Humans.
Therefore, it was only logical for the colonists of Vrantamire colony to seek help from the most stubborn badasses in known space. The Terran Space Marine Corps. They may be terrifying Deathworlders for whom death is cheaper than usual, but they were reliable and terrifying Deathworlders et cetera, et cetera. They came to do the job and then didn't have to be paid to leave.