When shooting them, you can see their parasites, they are orange. target them to kill this white monster.

soften with nades, target weak spot with pistol or spray orange spots with shotgun.

or just biosenor scope to target the parasites, this is found in the incubation lab which you can head to after using lv2 keycard to unlock the door in the area of "systems".
( NOT IN THE PLACE WITH NO POWER, AFTER YOU HAVE KEYCARD 2 YOU CAN USE IT TO GO TO THE LAB )


They stumble and "explode" when you manage a hit on their parasite, use high penetration weapons to kill the bugs inside them

And yes they do drop gems.