The world's worst pain comes from
bullet ant venom (shown above). According to Wikipedia, the pain caused by this insect's sting is purported to be greater than that of any other
hymenopteran, and is ranked as the most painful according to the Schmidt sting pain index, given a '4+" rating, above the tarantula hawk wasp and, according to some victims, equal to being shot, hence the name of the insect. It is described as causing "waves of burning, throbbing, all-consuming pain that continues unabated for up to 24 hours'. The pain is immediate and unlike even the worst physical injuries where your brain eventually has enough of it and blocks out the signal from the offending body part, it does not let go for a good long while.
Want to see someone some one bitten by one? Check out his reaction:
