Getting Into the Sting of Things

Content provided by the Faculty of the Harvard Medical School

Getting Into the Sting of Things

Venom from stinging insects can cause a bad allergic reaction, and some heart medications may make it worse.

The long days of summer lure many of us outdoors to take in some fresh air, soak up some rays, and — the health-conscious think to themselves — make some of that wondrous vitamin D. But alfresco, we also become prey for mosquitoes and other blood-hungry insects intent on making a meal out of us and spreading more than their fair share of pestilence in the process.

By contrast, stinging insects are a relatively minor matter from a public health standpoint. They don’t spread disease. Only about 40 Americans die each year from insect stings. But stings certainly hurt like the dickens, and for a small number of people, a sting unleashes a dangerous immunological reaction that’s anything but trivial. For people who suffer these strong reactions, heart medications like beta blockers and ACE inhibitors may make things worse.

Do not disturb

Bees, wasps, and fire ants are the most common stinging insects. They belong to the order Hymenoptera, which in Latin means “veil wing.” Leave them alone, and most members of the order will return the favor. In fact, as many of us learned in grade school science, honeybees are among the world’s most beneficial creatures, thanks to their pollinating behavior. Although bees have a splendid reputation as industrious, social creatures, many varieties are loners and aren’t likely to sting unless directly provoked. And the social ones usually sting only if their nest is threatened. Africanized honeybees, or so-called killer bees, in the South and Southwest are more aggressive than most bees and sometimes attack in swarms.

Wasps are a large, diverse family that includes yellow jackets and hornets. Like bees, some species can be solitary and relatively benign. But not yellow jackets, which relentlessly scavenge and often arrive at outdoor meals as annoying, uninvited guests. People occasionally swallow one that’s crawled into a beverage can. Never nice, yellow jackets become especially ornery during the late summer and early fall when their numbers increase and food supplies get scarce.

Hornets are larger than yellow jackets and build football-shaped nests in trees, and shrubs and under eaves. Some varieties are aggressive like yellow jackets, but others (Vespa cabro) aren’t, even though they’re bigger and scary-looking. Paper wasps build small, combed nests in eaves, behind shutters, and in woodpiles. Paper wasps have a reputation for being relatively tame unless bothered, but a new, fiercer species, Polistes dominulus, is displacing other ones.

Currently, fire ants are a problem in the Southeast and Texas, but their range is spreading. They build nests in the dirt, so people get stung when they inadvertently tread on a colony. One or two stings won’t faze most people, but often tens, even hundreds, of fire ants will attack at once if their nest is stepped upon. Their modus operandi is particularly nasty: The ant gets a good grip with its jaws, arches its back, and then jabs its rear stinger in. And given a chance, it will swivel around, delivering many stings in a circular pattern.

Classification of stinging insects *Although called a hornet, D. maculata is actually a type of yellow jacket. Photographs courtesy of Gary Alpert, Harvard University entomology officer. Red imported fire ant photograph courtesy of Brad Vinson at Texas A&M University.

Bite versus sting

Technically, a bite is delivered with the mouth or related structures, and a sting is delivered by a stinger, a needlelike structure at the other end of the body. Venom, the term for any injected toxin, can be delivered either way, but the etymologists believe stingers came about for defensive reasons, whereas the venom-filled bite evolved to paralyze prey.

Besides pain, stings cause swelling, redness, and itchiness. Some of this, especially the pain, is a direct reaction to toxic substances in the venom. The rest, particularly the redness and itchiness, is an allergic reaction — the body’s own immune system responding to an intruder.

Fortunately, these localized symptoms usually last only for a few hours (although it can be a long few hours), and an ice pack and some mild painkillers will relieve much of the misery. Elevating an affected limb may help reduce swelling. Over-the-counter hydrocortisone creams and oral antihistamines (Benadryl, Chlor-Trimeton) may help relieve the itchiness. Benadryl, in particular, can cause drowsiness, so don’t take it before driving or operating dangerous equipment.

Bee and wasp venom is a mix of enzymes, proteins, and various chemicals (vasoactive amines) that affect blood vessels. Fire ant venom is quite a bit different and contains piperidine alkaloids (the same chemicals that make hemlock poisonous). As a result, a fire ant sting doesn’t feel the same as other stings. Initially there is a painful burning sensation, followed by blistering.

Wasp and fire ant stingers are smooth, so those insects can wield their weapons, pull them out, and make a clean getaway. The important thing is to stay calm and to make a getaway yourself so you don’t get any more stings.

Bee stingers are barbed, so when a bee attacks, it pays a heavy price and leaves its stinger behind. Tiny structures designed to pump the venom through the shaft of the stinger also come off. So if you are stung by a bee, remove the stinger as soon as possible to avoid receiving more venom. An upward flick with a fingernail or credit card will do the trick. Using tweezers or your fingers can make a bad situation worse.

A shocked reaction

A few people have a more severe reaction to an insect sting. The symptoms range from hives (white swellings surrounded by areas of redness) and flushing to airway obstruction. In extreme cases, people experience anaphylaxis, a bodywide immunological response caused by a massive release of histamine. Anaphylaxis can lead to life-threatening shock. It’s difficult to predict who will respond this way because people who’ve tolerated insect stings in the past may respond differently in the future.

If you’ve had a serious reaction to an insect sting, you should see a doctor for an allergy workup. Skin and blood allergy tests aren’t perfect, but they can usually identify people who are allergic. Some people are treated with immunotherapy, which involves exposure to small but increasing doses of the venom over many years so the immune system eventually adjusts and doesn’t overreact when a real sting occurs.

A shot of adrenaline

People who are thought to be susceptible to anaphylaxis often carry an EpiPen, a self-injectable shot of epinephrine, also known as adrenaline. Epinephrine (pronounced ep-ih-NEF-rin) is a hormone associated with the body’s “fight or flight” response that causes your arteries to constrict (reducing swelling) and your lungs to relax (reversing the upper airway obstruction). But an EpiPen is a stopgap measure. Anyone who has occasion to use one should go to the emergency room as soon as possible for follow-up care.

People who are prone to insect allergic reactions and who also take beta blockers should talk to their doctor about switching to a different type of heart or blood pressure medication because beta blockers may prevent epinephrine from reversing anaphylaxis. Research also suggests that ACE inhibitors, another common class of heart disease and blood pressure medications, could pose a problem for people allergic to insect stings. Some studies have found that ACE inhibitors can heighten the allergic response to stings — and to venom immunotherapy designed to blunt that response. Researchers aren’t sure why, but ACE inhibitors may rev up certain inflammatory responses and keep the body from properly responding to epinephrine. It doesn’t appear to be a common problem, and no one is suggesting wholesale changes in prescribing practices. But if you’ve had a problem with insect stings and you’re taking an ACE inhibitor, you should discuss the possibility of a medication switch with your doctor.

Afraid? Don’t let it show

Of course, prevention is the best medicine. The stinging insects are attracted to brightly colored clothing — floral patterns can fool them — and sweet smells. So think about toning down your wardrobe if you’re headed out for a picnic. Alas, insect repellents aren’t very effective, but keeping food covered, especially if it’s sweet, may help keep yellow jackets from ruining your good time. If bees or members of the wasp family do pay visit (and they probably will) just stay calm. Shooing them away or waving your hands will only make them feel more threatened and likely to sting in retaliation. If you need to get rid of a small nest — if it’s large, we recommend calling a professional — do it early in the morning when the insects are less active. Wear thick gloves, a long-sleeved shirt, and some kind of goggles to protect your eyes.

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Last updated:	August 21, 2006
Reviewed By:	Faculty of Harvard Medical School