Several insects belonging to the class Hymenoptera are capable of injecting venom into humans and animals. These insects include honeybees, bumble bees, hornets, wasps, yellow jackets, and fire ants.

All of these insects are currently found in the United States as well as in most other land areas of the globe. Their venom, which they use to kill or paralyze other insects, is composed of proteins and other substances. It is proteins in the venom that cause allergic reactions in people.

Not everyone is allergic to stinging insect venom. In people who are not allergic, the venom causes only redness, itching, and mild pain and swelling at the site of the bite. Cleaning the area and applying ice are enough to relieve the symptoms.

Even people who are allergic to the venom usually have only mild symptoms, although the swelling may extend beyond the area right around the sting. People with allergy may have a more serious reaction, called an anaphylactic reaction. About 500 people die each year from anaphylactic reactions in the United States.

An allergic reaction occurs when the immune system of the body overreacts to an "invader" such as insect venom (the allergen). This overreaction is sometimes referred to as a hypersensitivity reaction. The white blood cells produce an antibody to the protein in the venom.

The allergic reaction occurs when the antibody, known as immunoglobulin E, or IgE, comes in contact with the protein, either at the first sting or later. IgE promotes release from certain cells of chemicals and hormones called "mediators." Histamine is an example of a mediator.

It is the effects of these mediators on organs and other cells that cause the symptoms of the allergic reaction. Ants, bees, and wasps have a stinger or venom sac and gland on their tail that they use to inject venom. Several stings may occur, particularly if you accidentally disturb a hive or nest.

This is particularly true with fire ants and so-called Africanized bees. Africanized bees are the result of breeding of domesticated and wild honeybees in Africa that resulted in a very aggressive honeybee. The venom of these bees is no more potent than that of normal honeybees, but their aggressive nature increases the likelihood that they will swarm and sting you many times, sometimes hundreds of times.

Such a large number of stings may result in serious reactions or death, even if you are not allergic to bee venom. If you are allergic to the venom, then you may have an allergic reaction from even a single sting. This is called an anaphylactic reaction. It can be dangerous, even life threatening.

An anaphylactic reaction does not usually occur on the first sting. The immune system makes the antibody at the first sting and stores it on special cells until the next sting. This is called sensitization. At the first sting, therefore, the body does not have antibodies specific to the venom.

Only on a second or later sting can the body mount a major defense against the venom. This is when a life-threatening anaphylactic reaction may occur. Anaphylactic reactions are rare, and do not happen to every person who is stung by an insect. When an anaphylactic reaction seems to occur on the very first sting, probably the person was stung before without realizing it.