The hemotoxic venom from this critter causes nausea, vomiting, necrosis, muscle and joint pain, the bursting of red blood cells, organ damage, and possibly death in young children with weak immune systems.
The lionfish announces its toxicity with its bold warning coloration. The venom, delivered through the fin rays, can cause a host of problems ranging from pain, vomiting and fever to convulsions, paralysis and even death.
The female black widow has large venom glands that deliver super-concentrated venom that interferes with the nerve signals that control muscles. The result is potentially fatal and causes severe pain and elevated blood pressure.
This critter's venom is so potent that it rivals the power of some snake venoms. The neurotoxins can cause intense pain, paralysis, asphyxiation and ultimately, death. Children are in particular susceptible.
The krait is particularly insidious because its bite may not cause any pain or even be noticed if a person is asleep. Its venom is full of powerful neurotoxins, though. A victim can literally suffocate to death four to eight hours after being bitten.
The potent venom of this spider is reputedly twice as deadly as cyanide. The effects on a human include increased blood pressure, arrhythmia, coma and death. The venom acts swiftly and can kill a small child within 15 minutes.
The boomslang can open its jaws as wide as 170 degrees when biting. Its venom is highly potent and contains a hemotoxin that disrupts a human's blood coagulation. That said, the venom is slow-acting, which helps buy time to obtain and anti-venom.
The Dubois has the deadliest venom of all sea snakes and can kill a mouse with one bite. Sea snake venoms are heinous. They can cause paralysis, blurry vision, difficulty swallowing or speaking, and, in about 3 percent of victims, death.
This highly toxic snake's venom affects both the nervous system and blood coagulation. If left untreated, mortality is 100 percent. In cases of severe envenomation, death comes swiftly -- within a half hour.
The aquatic snails may move slowly, but that's precisely why their venom is extra potent. They have hollow modified teeth called "radulae" that are sharp enough to penetrate a wetsuit, and the estimated human lethal dose is incredibly small -- it's believed that the venom in one of these mollusks is enough to kill 20 adult humans.
Although it's relatively small -- only the size of a golf ball -- its venom is debilitating and deadly. It can cause respiratory failure within 10 minutes and death within 30. One bite can kill up to 26 men, and there is no antidote.
Although the Australian box jellyfish just misses having the most potent venom on this list, it is probably the most deadly. It is large in size yet almost transparent in the water, and its tentacles can sting you with its millions of nematocysts, injecting a hefty amount of venom while holding its victim in place.
The venom's toxins can cause extreme pain, paralysis, delirium, shock, cardiac arrest and even death within minutes. The jellyfish has enough venom to kill 60 adults.