Larva
Primary Attack: None

Larva can morph into units.  Larva is created at the Hatchery.  Unlike other species, all Zerg units are morphed from Larva.

Drone
Primary Attack: Spines

Drones are used to gather minerals, gas, and morph into structures.  Once a drone morphs into a building, the Drone will not be there for you to use it again.  You'll have to get more Drones to morph into more buildings.

Overlord
Primary Attack: None

Overlords are used to transport units from one location to another.  Since Overlords are like Supply Depots, without them you cant morph anymore Larva until you're under the supply limit.

Zergling
Primary Attack: Claws

Zerglings serve as scouts and assault troops.  They are fast and can rip enemies to shreds.  Since they are so small and are so simple to replicate, one Larva can morph into two Zerglings.

Hydralisk
Primary Attack: Needle Spines

Hydralisk house hundreds of armor piercing spines within their carapace plates.  The spines can be fired in volleys.  Mass groups of Hydralisks should be approached with extreme caution.

Lurker (Brood War)
Primary Attack: Subterranean Spines

Lurkers are able to burrow and attack while underground.  They are extremely powerful in groups.  Any enemy caught in the spines will be impaled.

- Burrow
Zerg ground units except for the Ultralisk are able to bury themselves underground to hide and to ambush.

Ultralisk
Primary Attack: Kaiser Blades

The Ultralisk is the most powerful Zerg ground unit.  Their strong blades are use as battering rams against all ground units.  Ultralisks are extremely fast when upgraded.  They best way to approach this creature is from the air.

Mutalisk
Primary Attack: Glave Wurm

The Mutalisk's Acid Spray can burn through any armor.  They are the primary flying force of the Zerg.

Guardian Form
Primary Attack: Acid Spore

Guardians are one of the forms that Mutalisks can morph into.  Guardians are stronger in armor and attack, but their movement is slower.  They also have further range then Mutalisks.

Devourer (Brood War)
Primary Attack: Corrosive Acid

Another form that Mutalisks can morph into are called Devourers.  Devourers can only fire at air units.  The Acid Spores that are fired can slow down the enemies.  Enemies that are nearby may also be hit by the Acid Spores since it splashes.

Scourge
Primary Attack: Plasma metamorphosis

Scourges seek out air enemies and explode on them.  Of course, you lose that Scourge in the process.  Since their plasma is so powerful it can take out the strongest starship with a few scourges.

Queen
Primary Attack: None

Although the Queen does not produce Larvae, it has abilities to spawn parasitic creatures.

- Parasite
The Queen can parasite any enemy unit allowing the Overmind to see through the eyes of that enemy.  It can be removed by killing its host or using restoration.

- Spawn Broodling
Broodlings will attempt to fertilize any organic matter they come in contact with.  They are able to chew through any armor instantly resulting in death.

- Ensnare
The Queen can spray enemies with a thick mucous that slows down enemies.

- Infestation
The Queen is able to infest a damaged Terran Command Center and create Infested Terrans.

Infested Terran
Primary Attack: Suicide

Infested Terran produce extremely unstable chemicals.  They lock on to nearby enemies and detonate their own bodies causing major damage.  Infested Terrans can be created at an Infested Command Center.

Defiler
Primary Attack: Venom

Defilers are able to use deadly toxins against enemies.

- Dark Swarm
The Defiler can create a thick cloud of living insects that feed on themselves to provide cover for other Breeds.

- Plague
The Defiler can create corrosive spores that will damage all units caught within it midst for a period of time.

- Consume
The Defiler is able to feed off its own species to regain lost energy.