To me there are 3 versions of “worst” venom, which are: 1. the most likely to kill you, 2. the one that will be the most painful, and 3. the venom with no treatment. As a disclaimer I should say that, all bites or stings by venomous animals are very dangerous, and none of them are pleasant experiences!
For number 1, the most likely to kill you. Easily this is the box jellyfish. Most people stung by this don’t even reach the shore after being stung. Its venom affects the heart and the nervous system, causing them to shut down. It also causes incredible pain, causing most people to go into shock. Lucky survivors have reported feeling pain for weeks after a sting. Thinking about the animal itself, and what it uses its venom for, which in this case is catching fish, this all makes sense. Jellyfish generally float and can’t travel very fast, fish on the other hand are a lot faster. To catch a fish, they need to be killed (or otherwise incapacitated so they can’t swim) as quickly as possible. To do this, the venom targets the nerve endings called synapses, stopping neurons from carrying electrical signals, and so muscles such as the heart are paralysed. Unfortunately, whilst the venom is meant to target fish, all vertebrates have similar targets, which means that the venom also works against humans.
2. Causing the most pain. This can depend on the person obviously, but luckily for us…someone went around getting stung by things and made his own rating system. His name was Justin Schmidt who was an American Entomologist (works on biting insects). I quite like his way of describing the pain of bites and stings because it’s a lot like the descriptions you find on bottles of wine to describe how it tastes. His top choice was the sting of the bullet ant, which he described as “pure, intense, brilliant pain…like walking over flaming charcoal with a three-inch nail embedded in your heel”. Sounds lovely, doesn’t it? Some Brazilian tribes use these in coming-of-age ceremonies, where they make gloves out of leaves, with the insides completely covered with bullet ants. The trial is to shove your hands in and hope for the best. Apparently the pain can last 24 hours…
3. Lack of treatment. There’s actually a few animals where there is no treatment. From my background, the worst would be the Twig snake, which is from Africa. This snake is very similar to the Boomslang, although there is a treatment for this. The venom affects the blood clotting system, but its effects can be very slow (e.g. symptoms start several days after a bite), meaning people can think that they are fine but die several days later. It renders the blood incoagulable (i.e. it will no longer clot), causing internal bleeding.