You need to destroy all Electrofly Swarm in Bulletstorm single player campaign to unlock Pest Control achievement/trophy. These Electrofly Swarm are swarms of small blue flies. You need to get rid of 21 swarms to unlock this achievement/trophy.
Bulletstorm Electrofly Swarm Location Guide
Act II (Chapter 1)
Electrofly Swarm #1 – You will encounter the first swarm at the beginning of the chapter.
Electrofly Swarm #2 – Next one is after the fight near the inferno.
Electrofly Swarm #3 – It can be found after you have defeated the miniboss on the roof, head down and as you move out, you will find a cluster to the left.
Electrofly Swarm #4 – Last of this chapter can be found after you have met the girl. Reach down floor using the tree branch.
Electrofly Swarm #5 – Before you enter the dome, look right to find this group
Act III (Chapter 1)
Electrofly Swarm #6 – You can spot the first swarm just beside first dropkit.
Electrofly Swarm #7 – There is a half sunken craft near the final two boat docks. You will encounter one swarm on it’s bow.
Electrofly Swarm #8 – In the giant hall, there is a huge piano. There, you will find another Electrofly Swarm swarm in the perimeter.
Act III (Chapter 2)
Electrofly Swarm #9 – You will spot one group after you have dealt with creeps (after lowering the bridge).
Electrofly Swarm #10 – There is another one after the lengthy encounter with skulls and creeps.
Act IV (Chapter 1)
Electrofly Swarm #11 – Before the Venus Man-eater,look to the left side of the street.
Act IV (Chapter 2)
Electrofly Swarm #12 – After kidnapping, head right and keep going till you come across the Electrofly Swarm swarm.
Electrofly Swarm #13 – There is another swarm of Electrofly Swarm at the bottom of the steps ahead.
Electrofly Swarm #14 – While heading back up the steps, you will come across another Electrofly Swarm swarm after the 300 mark.
Electrofly Swarm #15 – One more can be found on the far side of the mausoleum.
Act IV (Chapter 3)
Electrofly Swarm #16 –Just beside the first dropkit.
Act V (Chapter 1)
Electrofly Swarm #17 – During the train repair, head to far side deck and look for the swarm. You will spot it on the left side.
Act V (Chapter 2)
Electrofly Swarm #18 – After the burnout encounter, you will find this group after kicking the door down the hallway.
Act VI (Chapter 2)
Electrofly Swarm #19 -After that scaffold cutscene, look down towards the pit for an Electrofly Swarm swarm.
Act VII (Chapter 1)
Electrofly Swarm #20 – You will spot one as you move outside the deep space cafe.
Electrofly Swarm #21 – Last Electrofly Swarm swarm can be found just after exiting the cargo bay.
Note. I will update for the missing Electrofly Swarm swarm locations tomorrow – so stay tuned.