Call of Duty: Black Ops III

Doable for the first time on round 5 :
The 5th round is the dog like round. You will have kinds of bees flying arround and shouting like scorpions (extinction mode). To earn the achievement you have to kill 5 bees when you are in the train and the train is moving.
Do do it easily ; By the end of round 4 kill the last zombie when you are in the train (there are 3 train stations arround the map). Wait until the first bees appears arround you and start the train (cost 500$). As soon as the train moves you start killing them, it will be easy as they are close to you ... while the train is moving make one or 2 additionnal kill and it is done. By the wait if you do not pop it, just restart the train once you are at destination.

According to MxSvnty4 : You do not even need the train to be moving. Just camp inside and get your kills.

Around round 5 these glowing bug zombies/creatures will spawn. They would be considered the dogs in the other cod zombie playlists. When they spawn, make your way towards the train.

You can either be riding the train and kill 5 of them or in my case the way that i got this achievement was that I was standing in the train (the train wasn't moving) and I still got this achievement.

The achievement is to kill 5 parasites, which are the flying green bugs, while riding on the train.

The parasites will arrive on round 5 if playing solo, sometimes later if playing coop.

Start the train once the parasites start spawning. If you don't kill 5 by time train stops, don't get off train. Finish killing and it'll pop.

I only killed 2-3 while it was moving and once it stopped I continued to kill and the achievement popped.

Get on the train at round 5 DO NOT MOVE IT just kill the 5 parasites by camping and the cheevo will pop after you kill the 5th one