In terms of the number of stings each year the Fire Ant is the most common ant that stings and has the potential to trigger a deadly dangerous anaphylactic reaction.
Fire ants (Solenopsis invicta) are restricted primarily to the United States and whilst there are naturally occuring fire ants it seems that the ones which cause the most allergy problems are the more recently introduced species, dating from around the 1920’s. These ants are slowly encroaching from their base in Texas to encompass all the southern United States – they are now encroaching northward and so are starting to become a real issue in the more densely populated areas of the US. They can now be found as far west as Nevada and as far east as Washington.
Fire Ant colonies are characterised by the mounds of soil generated above ground – a result of a network of tunnels under the ground which are used for hunting. The ants are very aggressive and will readily attack anything that disturbs their mound. After firmly grasping the skin with its jaws, the fire ant arches its back as it inserts its rear-end stinger into the flesh, injecting venom from the poison sac. It then pivots at the head and typically inflicts an average of seven to eight stings in a circular pattern. Fire ant venom is unique because of the high concentation of toxins, which are responsible for the burning pain characteristic of fire ant stings.
People are not just allergic to fire ant stings but also anaphylactic. Due to the obvious difficulties in collecting venom from fire ants (due to their size), venom immunotherapy, to be the best of my knowledge is not available for fire ants anaphylactics as a course of treatment. I understand that trials have been conducted using crushed up fire ant body parts but it would appear that this type of treatment was not particularly successful.
It would seem that the safest recourse for a fire ant allergic person is to avoid them by being very careful outside or by moving from their relatively limited geographical habitat. Otherwise protection and treatment is very similar to that recommended by for wasps and bees elsewhere in this site.