The Houdini Splicers are the enemies that teleport around and shoot fireballs at you.
Try and get a picture of them as soon as they come out of a teleport or are shooting a fireball at you or for even bigger bonus try and get pics of them fighting other enemies or even a Big Daddy.
You will need to fill the research bar 5 times for the achievement (also each time you fill the bar you will get a damage bonus against them).