Darkness Falls is a 2017 short story written by Heather Graham, published by Titan Books as part of the anthology novel Aliens: Bug Hunt. The story covers a Xenomorph outbreak on a verdant terraformed world where the creatures have gestated inside a giant breed of alien centipede.
On the planet Oleta, Police Chief Tarleton approaches one of the pristine terraformed world's residents, former Colonial Marine Captain Angela Hall, and informs her that there is an ongoing incident at the local mine, and that he suspects a Xenomorph may be involved. Knowing that Hall has had experience fighting Xenomorphs, Tarleton attempts to enlist her help in dealing with the situation, doubting that the colony's contingent of young, inexperienced Marines and their blustering commander, Lieutenant Colonel Simon Nicholson, will be able to contain the situation. When Hall refuses to become involved, Tarleton arrests her and takes her to the scene in his hover car.
Upon arriving, Tarleton's fears are confirmed — Nicholson refuses to accept a Xenomorph could be responsible, even when presented with security footage that appears to show a black-shelled creature tearing several miners apart, and sends his Marines without warning or proper tactics. The first wave sent inside the mine is quickly massacred. Learning that there are two young children trapped in the mine, Tarleton also rushes in, desperate to save them, while Nicholson sends in more Marines.
Nicholson is informed by his cousin Joe, also a Marine, that giant Blue Moon centipedes may have been introduced to the planet as a means of quickly and easily boring the mine tunnels, and that these creatures may have been the hosts for the Xenomorphs — unleashing a huge and incredibly dangerous version of the organism. When the second unit of Marines is also massacred, much like the first, Nicholson's bluster turns to shock and he loses all ability to command. Assuming command, Hall arms herself with a flamethrower and gathers a group of Marines to go into the mine and eradicate the Xenomorphs.
They discover the creatures have indeed gestated inside Blue Moon centipedes and are now giant, multi-legged specimens. Their flamethrowers are only moderately effective, but Hall manages to save one of the two children and escape the mine. However, the centipede-Xenomorphs follow her out and begin attacking the Marines on the surface. Remembering that centipedes are highly susceptible to salt, Hall and the Marine unit's android, Tommy II, formulate a plan to use a mechanical spreader to fire rock salt from the mine at the creatures.
While Tommy II prepares, Hall sees the other child emerge from the mine, pursued by more Xenomorphs. She rushes over to save him, realizing full well she will likely die in the process. Just as one of the centipede-Xenomorphs is about to bear down on her, Tarleton reappears and saves her, setting the creature ablaze with a flamethrower. Tommy II then arrives in the spreader and turns it on the Xenomorphs. As they had hoped, the creatures react violently to the substance, breaking down as it contacts them.
After all the Xenomorphs are destroyed, it is revealed that Nicholson's cousin Joe was responsible for bringing the Xenomorphs and the centipedes to Oleta; Tarelton arrests him. With the planet saved, Hall, Tarleton and the two children — revealed to be Tarleton's niece and nephew — head back to Hall's farm for breakfast.