An insect bite or sting often causes a small lump to develop, which is usually very itchy.
A small hole, or the sting itself, may also be visible. The lump may have an inflamed (red and swollen) area around it that may be filled with fluid. This is called a weal.
Insect bites and stings usually clear up within several hours and can be safely treated at home.
Different insect bites can cause different symptoms.
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 papular 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:
The Blandford fly
The Blandford fly (sometimes called blackfly) is usually found near rivers. It's common in:
- East Anglia
However, there have also been reports of Blandford fly bites occurring in other areas of England.
You're most at risk of being bitten by a Blandford fly in May and June. Bites often occur on the legs and are very painful.
They can produce a severe localised reaction (a reaction confined to the area of the bite) with symptoms such as:
- a high temperature of 38C (100.4F) or over
- joint pain
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. Otherwise, mites will bite any uncovered skin.
Spider bites from spiders native to the UK 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.
Spider bites leave small puncture marks on the skin, which can be painful and cause redness and swelling.
In severe cases, a spider bite may cause nausea, vomiting, sweating and dizziness. Very rarely, a spider bite may cause a severe allergic reaction.
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.
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, such as a bank card.
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, but 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 (LLR) – this can cause other symptoms, such as swelling, itching and a rash
- a systemic reaction (SR) – 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 it's rarely fatal.
Large localised reactions and systemic reactions are described in more detail below.
Large localised reaction (LLR)
If you have a large localised reaction (LLR) after being bitten or stung by an insect, a large area around the bite or sting will swell up. The area may measure up to 30cm (12in) across, or your entire arm or leg could swell up.
The swelling will usually last longer than 48 hours, but should start to go down after a few days. This can be painful, but the swelling won't be dangerous unless it affects your airways.
If you're bitten or stung many times by one or more insects, your symptoms will be more severe because a larger amount of venom will have been injected.
You may have an LLR several hours after being bitten or stung. This could include:
- a rash
- painful or swollen joints
Systemic reaction (SR)
You're more likely to have a systemic reaction (SR) if you've been bitten or stung before and become sensitised, particularly if it was recently. People who've been sensitised to bee stings are more likely to have an SR than people who are stung by wasps.