The Hymenoptera order is divided into three families: Apidae, Vespidae, and Formicidae. Apidae include the honeybee, bumblebee, and sweat bee, which are all docile and tend to sting mostly on provocation. The Africanized killer bee, a product of interbreeding between the domestic and African honeybee, is very aggressive and is mostly found in Mexico, Central America, Arizona, and California. The yellow jacket, yellow hornet, white (bald) faced hornet, and paper wasp all belong to the Vespidae family. The Formicidae family includes the harvester ant and the fire ant. When a "bee" sting results in a large local reaction, defined as >10 cm induration and lasting > 24 hours, the likelihood of anaphylaxis from a future sting is approximately 5%. For comparison, when there is a history of anaphylaxis from a previous Hymenoptera sting and the patient has positive skin test results to venom, at least 60% of adults and 20-32% of children will develop anaphylaxis with a future sting. Both patient groups should be instructed about avoidance measures and about carrying and knowing when to self-inject epinephrine, but immunotherapy with Hymenoptera venom is indicated for those patients with a history of anaphylaxis from the index sting and not for patients who have experienced a large local reaction. Immunotherapy is highly effective in that, by 4 years of injections, the incidence of subsequent sting-induced reactions is 3%. This incidence may increase modestly after discontinuation of injections but has not been reported to be > 10% in follow up.