This article is from the Children Allergies and Asthma FAQ, by Eileen Kupstas Soo firstname.lastname@example.org with numerous contributions by others.
In general there are three kinds of reactions to insect stings. The
first kind, normal reactions, involve pain, redness, swelling,
itching, and warmth at the site of the sting. The second kind,
toxic reactions, are the result of multiple stings. Five hundred
stings within a short time are considered likely to kill because of
the quantity of venom involved. As few as ten stings within a short
time can cause serious illness. Symptoms of toxic reactions include
muscle cramps, headache, fever, and drowsiness.
Allergic reactions are the third type. They may involve some of the
same symptoms as toxic reactions, but may be triggered by a single
sting or a minute amount of venom. Any non-local reaction to a
single sting should be considered allergic until proven otherwise.
Allergic reactions may be local or systemic. An allergic reaction
is considered local if it involves only one limb, regardless of the
amount of swelling. A slight systemic reaction may involve hives
and itching on areas of the body distant from the sting site as well
as feelings of anxiety and being run down. A moderate systemic
reaction may include any of the above plus at least two of edema
(swelling), sneezing, chest constriction, abdominal pain, dizziness,
and nausea. A severe systemic reaction has the symptoms already
described plus at least two of difficulty in swallowing, labored
breathing, hoarseness, thickened speech, weakness, confusion, and
feelings of impending disaster.
The most serious symptoms are the closing of airways and shock
(anaphylaxis) since they can be fatal if not treated quickly and
effectively. Allergic reactions may begin within ten to twenty
minutes after the sting or they may be delayed. Usually, the sooner
the reaction starts, the more severe it will be.