Let's see, you could look at "most poisonous" in different ways. For example, an animal might produce a very dangerous toxin but produce very little of it. Or it might produce a moderately lethal toxin and inject you with a lot of it. Some poisons might kill you quickly while others do horrible things like dissolve your flesh. So let's look at some of the poisons animals make and you decide which is the worst.

Basically, there are three ways poisons kill:

1. Neurotoxins interfere with how our nerves communicate with each other. No nerves means no movement and no feeling. Without working nerves, we can't breathe. Some jellyfish and their relatives (Cnidarians) have cells that use water pressure to shoot out barbed, poisonous extensions. Their poison attacks the membranes (outer coverings) of nerve cells. Many snakes use neurotoxins.

2. Proteolytic toxins actually destroy your flesh. ("Proteo" comes from the word protein, "lytic" means it breaks down.) Copperheads use this type of toxin. The site of the bite is almost sure to be lost, even with a small scratch. When the toxin reaches vital organs, death follows.

3. Some toxin triggers an allergic response. The body over-responds to a mild toxin and inflammation (swelling) closes the air passages. Bees, hornets, and wasps are famous for this.

If you want to check out a whole gallery of toxic animals, see this site:
http://www.aqua.org/information/media/species1.html
It contains pictures of many poisonous animals, including the black mamba, which can kill you with 2 drops of neurotoxic venom.

By the way, some animals, like the packrat (Neotoma spp.) are resistant to certain poisons.

Thanks for asking.

The most poisonous animal on earth? Black widow spider? Autralian black snake? Cone snail? Granddaddy longlegs spider? Scorpions? I dare say this question has many different answers that would all be correct, depending on how you interpreted the question! Here's why:

**If you want to know the animal that will kill you the quickest, then perhaps it is the highly poisonous box jellyfish, or sea wasp, that lives in the ocean. It's scientific name (Latin name) is Chironex fleckeri (pronounced KI-ro-nex fleck-er-I). This jellyfish is found most commonly near Australian beaches and in open ocean waters. Many swimmers have come in contact with it's tentacles and gotten badly stung. You can die from this poison in less than _three minutes_ if you get enough stings from the box jelly. The poison affects your nervous system by blocking specifically your Sodium-ion channels in your nerve cell membranes, or put more simply, it blocks nerve messages to and from your muscles causing eventual musculatory and respirtory failure. Most toxins that come from animals that I know about are neurotoxins like the one from box jellies. Doesn't sound like a great way to die, eh?

**If you want to know the animal that has the most deadly poison in the world, regardless of whether it injects you with enough poison to kill you or not, then it could bethe sea anemone, scientific name Palythoa toxica. Hawaiians used to coat their spears with this toxic sea animal to kill their enemies more quickly! If you extracted this toxin, then it would be more powerful (cause more deaths per volume of poison) than the poison made by the poisonous arrow frog (batrachotoxin) or the poison made by one-celled protozoans called dinoflagellates (saxitoxin).

If you want to know which organisms cause the most widespread poisoning, then the answer could be the dinoflagellates (pronounced Di-no-flaj-el-ates), which are individually very small (too small to see without a microscope! Around 40-50 micrometers in diamter) but multiply rapidly in certain marine ecosystems to create toxic "red tides". These blooms of dinoflagellates are neither very red, nor are related to the tidal cycle, but hey, everyone knows them by this common name! The dinoflagellate blooms usually make the waters look orange or pinkish, and concentrations of the dinoflagellate can reach 50-60 million per liter of water in coastal areas. WOW! Here's where the poison comes in: Each little dinoflagellate produces a toxin, called saxotoxin, that accumulates in animals that eat the dinoflagellates, like mussles and clams. People who eat the bivalves that accumulated this toxin via the digestion of dinoflagellates might get paralytic shellfish poisoning (PSP). People around the world die each year from this poison that gets more lethal as it travels up the food chain! Some dinoflagellate even release toxins into the water directly, causing huge fish kills and sick human swimmers in the same area. Dinoflagellates are very common in the oceans, so this is why I would label it the most widespread poisonous organism!

Some animals contain very dangerous poisons but in very small amounts in their bodies, and they only inject their prey with small amounts of poison at a time. Other animals are very dangerous because they are so aggressive in their behavior, and will bite or sting you with very little prodding! For instance, the blue ring octopus contains a very deadly poison, but it is not an aggressive animal, and divers can even play with it (carefully) without being stung. However, the boxjelly will sting you whenever it comes in contact with your skin, because it cannot tell human skin apart from its prey, which is usually little shrimp or fish.

While you think about _YOUR_ answer to the most poisonous animal in the world, here are some websites for you to puruse:

http://www.didaxinc.com/netschool/dangerous.html#TOP dangerous marine organisms?

http://ch.nus.sg/anatomy/html/toxin.htmlvirtual venom!

Humans can die from eating the PUFFER FISH, if it is not prepared correctly as sushi! The toxin that kills them is tetrototoxin:
http://www.biology.washington.edu/bsa/IonTransport/tetrodotoxin.html

CHIRONEX FLECKERI (SEA WASP)...you need a web translator for this unless you know German!
http://www.snafu.de/~froebel/tauchen/schrecken/wuerfelquallen.html

Good luck!