Symbiotes bond to a host organism in order to survive. When they bond to a host, they generally do so by forming a living costume or skin around the individual that can be retracted through the subject's skin. The symbiote and host share an empathic bond with each other, allowing the symbiote to react to the host's thoughts and emotions. Symbiotes feed off of the adrenal gland of their host, and because of this crave behaviors that will cause an adrenaline rush in the host creature. As a result of this the host will often partake in risky and violent behavior, and have a high mortality rate. A symbiote will generally have several hosts over their lifetime.

Powers

When a Symbiote bonds to a host creature, the host generally gains certain abilities through it. Some common abilities gained are:

Superhuman Strength

Superhuman Speed

Superhuman Agility

Healing

Genetic Memory: The host can bring back memories of former hosts of the symbiote.

Tracking: Generally in the form of tracking another symbiote.

Altering Appearance: They possess the ability to change their color as well as their shape. Toxin has exhibited the ability to also make certain portions of his body translucent or transparent (particularly at the eyes).

Tendrils: Flexible appendages that posses great amounts of strength equal to that of an average man.

Shape Shifting: Carnage has been known to create blades and other weapons on his limbs or change his very appearance or simply camouflage himself into his surroundings.

After being bonded with Spider-Man for so long, Venom also possesses the ability mask itself from Spider-Man's spider-sense.

Weaknesses

Even though each symbiote generation gets a little stronger their main weaknesses are sound and heat. Though some are more immune to the effects of said weaknesses, intense amounts will usually take a toll.

Notable Symbiotes

Venom - The Venom symbiote craved to bond with one host creature permanently rather than killing its host. Because of its views Venom was branded as a heretic by the rest of his species and was imprisoned. Spider-Man originally encountered the Venom symbiote during the Secret Wars, but removed it with the help of Mr. Fantastic when he learned that it was controlling his actions and attempting to bond with him permanently. Eddie Brock was the second and most memorable to wear the Venom symbiote. Brock had a strong hatred of Spider-Man, and as Venom became one of Spider-Man's greatest enemies. Currently Mac Gargan, the former Scorpion has bonded with the symbiote and taken up the Venom mantle.

Carnage - Carnage is the offspring of Venom. Carnage bonded with the insane Cletus Cassady, and is a dangerous enemy to both Spider-Man and Venom. Carnage can use his symbiote on his body to make a weapon, he can make his symbiote rock hard and when he flings some symbiote off, the symbiote can simply fall away in a few minutes.

Scream -

Toxin - The Toxin symbiote was the offspring of Carnage. Carnage tried to kill Toxin soon after spawning him out of fear of Toxin growing more powerful than both Venom and Carnage combined. Toxin bonded with police officer Patrick Mulligan, who is currently struggling to remain a force of good with his new found abilities.

Hybrid -

Alternate Realities

Earth-9997

On Earth-9997 (Earth-X) the Venom symbiote has bonded with an alternate version of May Parker - Spider-Girl. She is in control over it.

Earth-982

On Earth-982 (MC2) the Venom symbiote has bonded with Normie Osborn, grandson of Green Goblin. Much later the symbiote sacrificed itself to save Spider-Girl's life.

The Carnage symbiote was accidentally released by Spider-Girl from it's containment at SHIELD. It bonded to May's friend Moose Mansfield.

Earth-15

On Earth-15 the Carnage symbiote bonded with Spider-Man. His name is the Spider and is the member of the reality traveling Weapon X. He was killed by Firestar and was buried in his native universe.

Earth-928

On Earth-928 (2099) the Venom symbiote has bonded with Kron Stone, brother of Spider-Man 2099. It later bonded with Namor 2099.

Earth-9811

On Earth-9811 the Venom symbiote has been bonded with Spider-Man for so long that only his skeleton remains.

Earth-985

In this reality the Carnage symbiote bonded with Silver Surfer. The Surfer fought Spider-Man, the Avengers and Firestar. When she managed to injure the symbiote, he gained enough control of himself and realize what is happening. When he knew that the Carnage symbiote will likely to control him again, He flew towards the sun, destroying them both.