Insect Bite

Insect bites and stings

Insect bites and stings may cause minor pain and irritation but some may be extremely painful and may also trigger a serious allergic reaction.

In the United Kingdom common insect bites include mosquitoes, fleas, ants, midges, bedbugs, spiders, mites and ticks. The last three are not insects but arachnids.

Insects that may sting include bees, wasps and hornets. While an insect bites to puncture the skin often to feed on human blood, an insect stings as a defence and may inject venom into the skin. 1-5

What are the symptoms of insect bites & stings?

If an insect bites, it wets the area with its saliva. This may lead to an allergic reaction in the skin making the area around the bite to turn red, itchy and sometimes swollen.

After a sting too the venom causes a local allergic reaction to make the skin swollen, itchy and red and is termed a weal. The pain and itchiness may remain for a few days and is usually mild and harmless.

The severity of the reaction, however, depends on the sensitivity of the bitten person. If the person is allergic to the venom or to the bite there may be a mild to severe general allergic reactions. One such reaction is hypersensitivity reaction or anaphylaxis. This requires immediate medical treatment and even hospitalization to prevent death.

When to see a doctor?

A doctor needs to be consulted if the swelling and blistering covers large areas of the body or if there are other features like fever, pus formation (indicating infection) or allergic reactions with difficulty breathing, swelling of face and neck etc.

The following signs should see a doctor as soon as possible:

  • nausea

  • vomiting

  • diarrhoea

  • rapid heart rate

  • shallow breathing

  • difficulty swallowing

  • rapid fall of blood pressure

  • shock

  • confusion

  • agitation

What is the treatment of insect bites and sting?

The most common treatments may be done at home and are usually enough to cure the symptoms.

The affected area needs to be washed with soap and water to remove the allergenic venom or sting. The sting, if visible may be removed before washing or any treatment is attempted. A cold compress may be placed over the area to reduce the swelling and ease the pain. Pain relievers like Paracetamol or Ibuprofen may be taken.

Those with a more serious allergy usually need therapy at the hospital. Those with anaphylaxis or severe allergies may need to be given adrenaline injection as an emergency life saving measure and may need hospital admission.

How can insect bites and stings be prevented?

Insect bites and stings are common if time is spent out of doors especially in the wild. Common measures to prevent bites include wearing covered clothes, wearing or using an insect repellent, staying indoors after dusk and using insect screens etc. Avoidance and backing away gently from stinging insects like bees, wasps and hornets helps prevent stings.

Those travelling abroad like Africa, Asia and South America are at risk of insect bites like mosquito bites that may transmit malaria and other diseases like:

  • Yellow fever from mosquitoes in Venezuela

  • relapsing fever and Chagas disease from bed bugs in Mexico

  • Lyme disease and Rocky Mountain spotted fever from ticks in eastern US states

Other insect bourne diseases include dengue, onchocerciasis, trypanosomiasis, leishmaniasis and loiasis.

Necessary precautions, medication or vaccination before travel is essential. Studies have shown no evidence of HIV transmission through mosquito or other insect bites however.

Symptoms of insect bites

Insect bites commonly cause mild symptoms of redness, itching, swelling and irritation. A bite may be a small puncture in the skin around which there is redness and itching while a sting is a swelling with a small puncture that consists of the sting which may be visible. The lump may have an inflamed area around it filled with fluid and may be called a weal.

The bites usually resolve in a few hours and may be managed easily at home. However, there are some warning symptoms that need to be watched out for and medical help should be sought if these symptoms are encountered. (1-6)

Allergic reactions to insect bites

Allergic reactions to the bites and stings may be:

  • Minor localised reaction

This leads to pain for a few days but resolves with home management. There is patch of redness and a small area of swelling (up to 1 cm) around the bite or sting that goes away in a few hours.

  • Large localised reaction

There may be generalized rash, swelling and itching or urticarial. The area around the bite or sting or the entire limb may swell up. The swelling will usually last longer than 48 hours. More bites or stings lead to more severe reactions.

  • Generalized or systemic reaction

This is severe form of allergy that leads to anaphylaxis. The patients have usually been bitten or stung once when their body is sensitized to the bite or sting.

Patient is wheezing, breathless, has a rapid pulse rate, rapidly falling blood pressure, nausea, vomiting and diarrhea, swelling of the face, neck and lips and confusion, anxiety or agitation.

General symptoms of insect bites

The general symptoms that occur from insect bites depend on the type of insect.

Symptoms of bites from mosquitoes, ants, midges and gnats

Bites from mosquitoes, ants, midges and gnats lead to small lumps over the skin. These are very itchy since the skin may be allergic to the saliva of the insect that it spreads over the skin before it bites.

Those who are allergic may develop fluid-filled blisters or bullae or circular, fluid-filled areas around the bite (weals) in response to bites from mosquitoes, ants, midges and gnats.

Symptoms of bed bug bites

These are usually mild and lead to minor irritation of the skin. The bits commonly affect the face, neck, arms, legs etc.

Symptoms of flea bites

Flea bites usually occur in small clusters. Those who are allergic to flea bites may develop several itchy lesions called papular urticarial. Blisters or bullae may also form.

Flea bites from pets usually affect below the knees commonly around the ankles. However, forearms may also be affected while holding the pet animal.

Symptoms of bites from horseflies

Horseflies may bite to form a painful weal. Hives, welts or nettle rash may develop as an allergic reaction.

Patient may develop severe allergic reaction as manifested by weakness, dizziness, wheezing, swelling around the eyes and lips called angioedema etc. These bites are bigger than other insects and may get infected and take a long time to heal.

Symptoms of bites from the Blandford fly or black fly

The Blandford fly or black fly is found in East Anglia, Oxfordshire and Dorset. This bites during May and June and may lead to painful lesions in the legs. There may be severe swelling, blisters, pain, joint pain and fever as a reaction to the bite.

Symptoms of tick bites

Ticks (Ixodoidea) are not insects but arachnids. These may leave red lumps where they bite. Allergic individuals may develop itchiness, blisters and bruises.

Ticks may transmit diseases like bacteria Borrelia burgdorferi which causes Lyme disease. In the UK, most common ticks on humans are sheep tick (Ixodes ricinus), and hedgehog tick (Ixodes hexagonus).

Symptoms of mites bites

Mites may bite to leave itchy lumps or blisters. These are common among pet owners. Harvest mites (Tromboculidae) may bite during late summer and usually the larvae of the harvest mite (Neotrombicula autumnalis) attach to the skin under tight-fitting clothes, feed and then detach. This leads to itchy lesions or bullae.

Symptoms of spider bites

Spider bites may also lead to intense pain, swelling and redness. Severe allergic reactions may also be seen with some spider bites.

Wasps, hornets and honeybees stings

This is usually a defence reaction of the insect rather than a bite. The sting causes sharp pain in the area. On the skin there may be a swollen red are with the sting visible on it. The area is painful and itchy.

Bee stings initially feel like wasp or hornet sting. The venom however may spread and lead to an allergic reaction.

Treatment of insect bites

Insect bites usually cause mild irritations and can be managed safely at home. The bites and stings lead to small localized reactions that remain confined to the area around the bite or sting. However, large localized reactions or generalized allergic reactions need to be seen and treated by physicians. 1-5

The first step is to move to a safer area to avoid more stings or bites.

Removal of an insect sting

When visible a bee or wasp sting may be removed carefully. Bees usually leave the sting behind but a wasp or hornet may not leave the sting behind and may sting again. If attacked by a wasp or hornet one should walk away calmly to avoid being stung again.

Care should be taken not to rupture the venom sac within the sting that results in spread of the venom and severe pain and allergic reaction. The sting can be removed by scraping it out with long finger nails or with a hard edged card.

The sting should not be squeezed of held with tweezers as it may rupture the venom sac and release the venom into the skin. If a child has been stung, an adult should remove the sting.

Basic home measures to treat insect bites and stings

Minor bites and stings with localized reactions may be treated with basic home measures. The local area should be washed with soap and water to remove the allergenic saliva. Thereafter a cold compress may be placed over the area to ease the pain and swelling.

The bitten child or person is advised not to scratch as this may lead to infections. The fingernails should be kept clean and short and filed to avoid skin injury.

Avoiding infections from insect bites

Blisters and bullae should not be burst as these may develop infections and open sores. An adhesive bandage or plaster may be used to protect the area.

Treating infected insect bites

If the bites are infected antibiotics may be prescribed. Severe infections may need antibiotic pills prescribed by a doctor.

Relieving pain caused by insect bites

For painful stings an ice pack may be applied. Pain relievers like Paracetamol, Ibuprofen etc. may be taken for the pain and inflammation. Some over the counter sprays or creams with antihistaminics (reduce the allergic reaction), local anesthetic (numbs the area) or steroid (hydrocortisone 1% for inflammation) may be used to prevent itching and swelling.

Crotamiton ointment (available at pharmacies), calamine lotion, or a baking soda paste are soothing as well. Antihistaminic or allergy reducing tablets may be taken to reduce the allergic reactions.

Treatment for a large localized reaction

Those with a large localized reaction may require a prescription of a short course of steroids like prednisolone pills to be taken for three to five days. Those with severe generalized reactions like anaphylaxis may need adrenaline injections, oxygen and fluids.

Treatment for severe allergic reactions

Those with a severe allergic reaction that extends with a redness and swelling of over 10cm (4 inches) in diameter may need evaluation at an allergy clinic. These patients may be advised Immunotherapy (desensitisation or hyposensitisation) to reduce their risks of developing an allergy to the sting.

Treating ticks

The tick usually clings to the skin. Ticks are removed using tweezers after wearing gloves to avoid exposure of the fingers to the tick. The tick should be removed as a whole and while removing care should be taken not to break it off so as to leave behind the mouthparts of the tick within the skin.

If this does not work petroleum jelly, alcohol or a lit match may be used to remove the tick.

After removal hands should be washed with soap and water and the area should be washed with soap and water or an antiseptic. Those with a rash or fever may have acquired Lyme disease that are carried by ticks and may need evaluation and treatment.

Complications of insect bites

Insect bites or stings may lead to mild irritation, itching, redness and swelling and may often go away within a few hours. In some cases however there may be complications after being bitten or stung by the insect. 1-5

Common complications include allergic reactions, secondary infections and so forth.

Allergic reactions to insect bites

Allergic reactions like rashes, hives, nettle rash, facila swelling (angioedema) may be seen.

Severe allergic reactions or anaphylactic shock may be potentially life threatening. Symptoms include breathing problems, rapid fall in blood pressure, shock, swelling and constriction of the air passages, swelling of the face, lips and neck etc.

Secondary infections

Insect bites or stings may often be itchy and repeated scratching may lead to skin abrasions and predispose to skin infections. Some of the skin infections may manifest as sores and blisters that are often filled with pus. This is called impetigo.

An inflammation and pus point may often affect hair follicles of the skin and lead to folliculitis. When large areas of skin and underlying tissues are affected, it is called cellulitis.

If the infection spreads to the lymph nodes of the armpits, groin or neck, it is termed lymhangitis.

While folliculitis and impetigo may be treated with locally applied antibiotic creams and ointments, more generalized infections like cellulitis or lymphangitis may require oral antibiotic pills.

Lyme disease

This is borne by a species of tick known as Ixodes ricinus. There are around a thousand new cases of this disease in England and Wales every year. There may be a red rash at the site of the bite that spreads gradually.

Antibiotics are usually used to treat the infection. If left untreated Lyme disease may affect the central nervous system and lead to complications like facial weakness or paralysis, meningitis or encephalitis.

Lyme disease over long term may also lead to joint problems like arthritis and heart muscle problems like myocarditis. The tissue layer that cover the heart called the pericardium may also be inflamed (pericarditis) with Lyme disease.

West Nile virus infection

This virus is carried by mosquitoes. Usually there are influenza like symptoms of fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph nodes or a skin rash. Complications include encephalitis and meningitis and may manifest with seizures.


Malaria is a parasitic infection that is carried by mosquitoes. It is common in hot and humid climates. Travellers to tropical countries often bring back the infection to more developed and cooler countries.

Malaria is manifested with fever, chills and rigor and may lead to severe complications and even death without treatment. There are two main types of malaria infection with Plasmodium vivax and Plasmodium falciparum. Infection with P. Falciparum is potentially life threatening if not detected and treated early.

Rocky Mountain Spotted Fever

Rocky Mountain Spotted Fever is caused by bacterium Rickettsia rickettsii that is transmitted by infected ixodid (hard) ticks. There are three main symptoms of fever, rash, and history of tick bite.

There may be nausea, vomiting, severe headache, and loss of appetite, pain in the abdomen, muscle aches and diarrhoea. After initial 2 to 5 days there may be a red rash on the wrists, forearms, palms, soles and ankles.

Other insect borne diseases

Other insect borne diseases include:

  • relapsing fever and Chagas disease transmitted by bed bugs in Mexico
  • Yellow fever transmitted by mosquitoes
  • Dengue fevertransmitted by mosquitoes
  • onchocerciasis by black flies
  • trypanosomiasis by tsetse flies or by reduvid bugs
  • leishmaniasis transmitted by sandflies
  • loiasis by Deer flies or Mango flies
  • Ross River fever by mosquitoes