INFESTED
The original small, worm-like creatures known as Zerg were genetically maniuplated by the Xel'Naga, and developed the ability to burrow into the flesh of other, more powerful species that dwelt upon their home planet of Zerus. Feeding off spinal fluids, the Zerg learned to parasitically merge with their hosts, becoming capable of controlling their bodies and manipulating their surroundings. The Zerg incorporated more and more host creatures into their fold, and began to assimiliate their genetic strains and processes. All Zerg genetics began to adapt to the new material being processed, though the Zerg sought out only the most evolutionarily advanced species to assimiliate.
All races assimiliated by the Zerg mutate, gaining carapaces, armor piercing spines, and razor-sharp limbs. No matter what the creature originally looked like, it is always easily identified as being part of the Zerg race now.
Infested creatures speak any languages they knew before becoming infested.

CREATING AN INFESTED CREATURE
“Infested” is an acquired template that can be added to any non-undead, non-outsider creature (referred to hereafter as the base creature).
An infested creature uses all the base creature’s statistics and special abilities except as noted here.
Size and Type: The creature’s type changes to abberation (Zerg). Do not recalculate base attack bonus, saves, or skill points. Size is unchanged.
Speed: Same as the base creature. If the base creature is land-based, the infested creature also gains a 10 ft. burrow speed.
Armor Class: The base creature’s natural armor bonus improves by +2.
Attack: An infested creature retains all the attacks of the base creature. A creature with natural weapons retains those natural weapons. An infested creature armed with a weapon uses its natural weapons or a weapon, as it desires. Some creatures may gain additional natural attacks, depending on their form (DM's discretion).
Full Attack: An infested creature fighting without weapons uses its natural weapons (if it has any). If armed with a weapon, it usually uses the weapon as its primary attack along with a natural weapon as a natural secondary attack.
Damage: If the base creature had natural weapons, they are now considered adamantine (in addition to any other properties they may have had) for the purposes of overcoming damage reduction.
Special Attacks: An infested creature retains all the special attacks of the base creature. It may gain additional special attacks, at the DM's discretion. Save DC's are 10 + 1/2 the infested creature's HD + the infested creature's Constitution modifier.
Special Qualities: An infested creature retains all the special qualities of the base creature and gains those described below.
Adaption (Ex): An infested creature no longer needs to sleep or breathe, and may exist in space with no ill effects.
Fast Healing (Ex): An infested creature gains fast healing equal to its Constitution modifer.
Hive Mind (Ex): An infested creature is always aware of what all other Zerg within 50 ft. of it are doing.
Immunites (Ex): An infested creature is immune to poison and cold.
Resistances (Ex): An infested creature has resistance to acid 15 and electricity 15.
Abilities: Increase from the base creature as follows: Str +4, Dex +2, Con +4, Wis +2, Cha -4. The creature's intelligence drops to 1; it is now almost mindless, blindly obeying all commands from its Cerebrate.
Skills: Infested creatures recieve a +4 racial bonus on Listen and Hide checks while underground. Otherwise same as the base creature.
Feats: Same as base creature.
Environment: Any, usually same as base creature.
Organization: Same as the base creature.
Challenge Rating: Same as the base creature +2.
Treasure: Same as the base creature
Alignment: Always lawful evil
Advancement: By character class.
Level Adjustment: Same as the base creature +4.