Allergic reactions to fire ant stings are due to proteins present in tiny amounts in the venom. These proteins, Sol i1, Sol i2, Sol i3 and Sol i4 are capable of triggering an allergic response. Sol i1 is about 3% of the total venom protein and it has phospholipase activity that can degrade cells. One half to two thirds of the venom protein is Sol i2. Sol i3 has substantial homology to an antigenic venom protein from a yellow jacket, Vespula vulgaris. People who have allergies to yellow jacket stings are more likely to be allergic to fire ant stings.
People with known allergic reactions to fire ant venom can have immunotherapy based on exposing patients to small doses of fire ant protein. The success of immunotherapy improves with our knowledge of venom toxins and the ability collect or produce them in large enough quantities. The quality of proteins used in immunotherapy is important in making reactions to fire ant stings less severe.