Since they are grouped together you should be able to slash a few at a time killing multiple enemies quickly while only using one bullet. When they are on the ground simply knife them. When you are low on ammo but have to kill a few enemies try to group them together, shoot the frontman of the group in the head making him stumble then, run up and kick, this should knock down or push back all of the enemies.
They can also be sold separately for easy money. It will go to a cutscene where it shows the hive fall into the pit and after there are about 10 items you can pick up, all of which are the 'red, green, or blue eyes' used on the Butterfly Lamp. If you have the patience to kill all the enemies, shoot the hive type thing in the middle of the room. You must shoot the chains to drop a bridge.
After you set down the King and Queens grail you come to a part where there are a bunch of the 'bug' type enemies.
