Symptoms of an insect bite or sting
Insects that bite include midges, mosquitoes, fleas, bedbugs and, although not strictly insects, spiders, mites and ticks, which are arachnids. Insects that sting include bees, wasps and hornets.
An insect bites you by making a hole in your skin to feed. Most insects sting as a defence by injecting venom into your skin.
The severity of bites and stings varies depending on the type of insect involved and the sensitivity of the person.
In rare cases, some people can have a serious allergic reaction (anaphylaxis) to a bite or sting that requires immediate medical treatment.
The symptoms that can occur from different types of insect bites are described below.
Midges, mosquitoes and gnats
Bites from midges, mosquitoes and gnats often cause small papules (lumps) to form on your skin that are usually very itchy. If you're particularly sensitive to insect bites, you may develop:
- bullae – fluid-filled blisters
- weals – circular, fluid-filled areas surrounding the bite
Mosquito bites in certain areas of tropical countries can cause malaria.
Flea bites can be grouped in lines or clusters. If you're particularly sensitive to flea bites, they can lead to a condition called popular urticaria, where a number of itchy red lumps form. Bullae may also develop.
Fleas from cats and dogs can often bite below the knee, commonly around the ankles. You may also get flea bites on your forearms if you've been stroking or holding your pet.
A bite from a horsefly can be very painful. As well as the formation of a weal around the bite, you may also experience:
- urticaria – a rash of weals (also called hives, welts or nettle rash)
- angio-oedema – itchy, pale pink or red swellings that often occur around the eyes and lips for short periods of time
Horseflies cut the skin when they bite, rather than piercing it, so horsefly bites can take a long time to heal and can cause an infection.
Bites from bedbugs aren't usually painful, and if you've not been bitten by bedbugs before, you may not have any symptoms.
If you have been bitten before, you may develop intensely irritating weals or lumps.
Bedbug bites often occur on your:
Tick bites aren't usually painful and sometimes only cause a red lump to develop where you were bitten. However, in some cases they may cause:
Ticks can carry a bacterial infection called Borrelia burgdorferi, which causes Lyme disease. Lyme disease can be serious if it isn't treated.
Mites cause very itchy lumps to develop on the skin and can also cause blisters. If the mites are from pets, you may be bitten on your abdomen (tummy) and thighs if your pet has been sitting on your lap. Mites will bite any uncovered skin.
Spider bites from spiders native to Northern Ireland are rare. You’re more likely to be bitten by a spider while you're abroad, if you keep non-native spiders as pets, or if you have a job that involves handling goods from overseas.
Bites can be from a venomous or non-venomous spider. A bite from a non-venomous spider will often cause minor swelling, redness, pain, and itching. These mild reactions are common and may last from a few hours to a few days.
Very rarely, a spider bite may cause a severe allergic reaction.
A few people have severe reactions to the toxin injected by the insect or spider.
See section ’ When to seek medical help’ below – this highlights symptoms that require urgent medical care.
Wasps and hornets
A wasp or hornet sting causes a sharp pain in the area that's been stung, which usually lasts just a few seconds.
A swollen red mark will often then form on your skin, which can be itchy and painful.
Wasps and hornets don't usually leave the sting behind, so they could sting you again. If you've been stung and the wasp or hornet is still in the area, walk away calmly to avoid being stung again.
A bee sting feels similar to a wasp sting, but the sting and a venomous sac will be left in the wound. You should remove this immediately by scraping it out using something with a hard edge that is clean (to avoid introducing infection)
Don't pinch the sting out with your fingers or tweezers because you may spread the venom.
Most people won't have severe symptoms after being bitten or stung by an insect. However, some people can react badly to them because they've developed antibodies to the venom.
You're more likely to have an allergic reaction if you're stung by an insect. The reaction can be classed as:
- a minor localised reaction – this is normal and doesn't require allergy testing, although the affected area will often be painful for a few days
- a large localised reaction– this can cause other symptoms, such as swelling, itching and a rash
- a systemic reaction– this often requires immediate medical attention because it can cause a potentially life-threatening allergic reaction (anaphylaxis)
Although insect bites and stings are a common cause of anaphylaxis, it's rare to experience anaphylaxis after an insect sting, and insect bites or stings are rarely fatal.
Insect bites can sometimes become infected. Symptoms of an infected insect bite may include:
- pus in or around the bite
- swollen glands
- increased pain, swelling and redness in and around the bite
Some bites will be red and swollen, but for other types of bites these symptoms may not be normal and could suggest an infection.
Treating insect bites and stings
Most bites and stings are treated by:
- washing the affected area with soap and water
- placing a cold compress (a flannel or cloth soaked in cold water) over the area to reduce swelling
Try not to scratch the affected area to avoid infection. If you're in pain or the area is swollen, take painkillers such as paracetamol or ibuprofen (children under 16 years of age shouldn't be given aspirin).
The pain, swelling and itchiness can sometimes last a few days. Ask your pharmacist about over-the-counter treatments that can help, such as creams for itching and antihistamines.
If you have a more serious reaction, your GP may prescribe other medication or refer you to an allergy clinic for specialist assessment and treatment.
When to seek medical help
You should see your GP if you've been bitten or stung and there's a lot of swelling and blistering or if there's pus, which indicates an infection.
Dial 999 and ask for an ambulance if you experience any of these symptoms after a bite or sting:
- wheezing or difficulty breathing
- nausea, vomiting or diarrhoea
- a fast heart rate
- dizziness or feeling faint
- difficulty swallowing (dysphagia)
- confusion, anxiety or agitation
Preventing insect bites and stings
You're more likely to be bitten or stung if you work outdoors or regularly take part in outdoor activities, such as camping or hiking.
Using insect repellent and keeping your skin covered when outdoors will help you avoid being bitten or stung.
Try not to panic if you come across wasps, hornets or bees, and back away slowly. Don't wave your arms around or swat at them.
There's a risk of catching diseases such as malaria from insect bites in certain parts of the world, such as:
- South America
It's therefore important to be aware of any risks before travelling to these areas, and to get any necessary medication or vaccinations.
- Find out more about insect bites and stings on the NHS website.