You explain how the dominant species here has been hunted to dangerously low levels by a race of insectoid creatures from a nearby star system. The locals aren't advanced enough for interstellar travel and are hopeless to repel the invader, so that's why you're here. Having heard your brief dialogue, the team suits up and packs on some heavy guns.
"Alright, soldiers," Captain Steele belts, "Who's ready to shoot some bugs?" Everybody responds with a loud affirmative and it's off to the transporters to beam down to the surface of the planet. You're going in two teams, but there's an odd number of you, so you get to pick which job you want.