|Blue ringed octopus. Photograph by Roy Caldwell via Wikimedia Commons|
The terms poisonous and venomous are not interchangeable. Venomous creatures produce a biotoxin and inject it by means of bite, sting, or other sharp protruding body part (such as spines or spurs). Utilization of venom occurs across a broad spectrum of classifications, from invertebrates (spiders) to fish (stonefish) to mammals (male platypus). Venom can be used as both an offensive and defensive weapon.
Lists of "most venomous" animals vary, due to differences in criteria. Are they rating absolute toxicity? Most commonly encountered? Highest death toll among humans? I thought I'd list a few with no known antidote; you get envenomated, you probably die in a painful and horrible manner.
1. The Blue-Ringed Octopus is strikingly beautiful and small, but its venom is powerful. It carries enough poison to kill 26 adult humans within minutes, and there is no antidote.
2. The Pufferfish's poison produces a quick and violent death. Puffer poisoning causes dizziness, vomiting, rapid heart rate, difficulty breathing, and muscle paralysis. Victims die from suffocation when diaphragm muscles are paralyzed. There is no known antidote.
3. Coral cobra. These snakes are not true cobras but get their name from both their color and habit of flattening their necks into a hood. They are native to Africa and are highly venomous. However, since they have short fangs and live a burrowing lifestyle, the chances of a deadly encounter are fairly slim. There is no known antidote for their bite.
4. Cone snails typically live in warm and tropical oceans worldwide, with the highest density in the western Pacific region. They have beautifully patterned shells, but carry a deadly neurotoxin with which they poison their prey. Symptoms after being stung include typical neurological impairment such as weakness, lack of coordination, vision problems, and difficulty with speech and hearing. A heavy dose of venom from one of the larger snails may result in death, due to respiratory paralysis, within hours. There is no antidote.
5. Box jellyfish show up on nearly every list. Most entries I've read state that there is no antidote to the poison. However, it's my understanding that an antidote does now exist. Unfortunately, many victims probably wouldn't live long enough to take advantage of it anyway.
Box jellies include about 50 described species; there are probably more yet to be discovered. They have tentacles covered in tiny cnidocysts; each one is like a poison dart that causes an immediate and explosive release of poison. The toxin enters the blood, spiking blood pressure to dangerously high levels and often causing cardiac arrest.
That's a short list, due to the nature of the A to Z Challenge. (I've tried to keep my posts short and sweet.) There are plenty more venomous - and deadly - creatures out there. But let's not forget that in studying these toxins and attempting to find antidotes, scientists have learned a great deal about how toxins work, and they have also put these toxins and/or their components to work saving lives.