Insects typically inject formic acid. This can lead to blisters, inflammation, redness, swelling, pain, itching, and irritation.
The reaction depends on the type of insect and the individual's sensitivity.
Bites from fleas, mites, and mosquitoes tend to cause itching rather than pain.
- Many different insects can bite, and the effects of their bites can range from mild irritation to a deadly infection, such as malaria.
- Spiders are not insects, but they can deliver a painful and troublesome bite.
- If a person starts to have breathing difficulties and swelling, they need urgent medical attention.
- Most bites can be soothed with an over-the-counter treatment.
- Use insect repellant and clothes that cover the body to prevent insect bites during outdoor activities.
Which insects bite?
The effect of an insect bite can range from mild irritation to a serious disease.
In the northern United States and Canada, biting insects include:
- flies, such as horseflies
In the southern states, there may also be sand flies.
Spiders are not strictly insects, but they can also bite.
Individuals react in different ways. A bite that causes a small, itchy lump that disappears in a few days in one person can have a more serious effect on another.
If a bite becomes infected, there may be redness, warmth, and hardening of the surrounding skin, with pus draining from the wound.
Scratching the wound can lead to infection, and it can cause the skin to become thick and leathery skin. This is called "lichenification."
People who work outdoors or regularly participate in outdoor activities are more susceptible to insect bites.
Insect bites normally cause a small itchy lump to develop on the skin. Sometimes the bite itself may be visible, as a tiny hole. The lump may be filled with fluid. The area around the lump is sometimes inflamed.
Insect bites normally disappear within a few days without medical attention.
Some people may have an allergic reaction to insect bites, but bites rarely cause a severe allergic reaction, unlike insect stings.
The following may indicate a severe allergic reaction:
- a rash, often blotchy, can spread to other parts of the body
- breathing difficulties
- chest pain
- faintness or dizziness
- rapid heartbeat
- severe swelling, which may be far from the bite area, such as the tongue or lips
- very severe itching
These symptoms require immediate medical attention.
Some people may have a stronger reaction the second time they are bitten by a particular type of insect. This is called sensitization. The individual becomes more sensitive to the insect's saliva.
An infected insect bite can lead to:
- pus inside or around the bite
- swollen glands
- a feeling of being unwell
- flu-like symptoms.
The bite area may become redder with more pain and swelling.
An itchy papule or wheal may develop and persist for several days. Eventually, most people become immune and insensitive to the saliva, after being bitten a number of times.
Insect bite reactions do not normally last more than a few hours, but sometimes they can linger for months. In this case, the individual should consult a doctor.
The brown recluse spider can inflict a damaging bite.
Spiders are not insects, but they can bite. Some spider bites are quite dangerous to humans.
The bite of the brown recluse produces only a mild sting at the time of the bite, but it can be very damaging, causing tissue destruction and severe pain.
Redness develops in the bite area, and pain may become intense within about 8 hours.
A fluid-filled blister forms at the puncture site. The blister then sloughs off, leaving a deep, enlarging ulcer.
Sometimes, this ulceration goes away without any further problems, but sometimes this ulceration spreads or becomes superinfected by bacteria.
Symptoms include a mild fever, listlessness, nausea, and sometimes a rash. Death is rare but possible, especially in small children. You should seek medical attention if you believe that you have been bitten by a brown recluse and have a spreading ulceration or redness/infection of the area.
The black widow is the most venomous spider in the U.S., but its bite is rarely deadly. The bite feels a pinprick in the skin. There may be slight a swelling and faded red marks, but within a few hours, stiffness and extreme pain may develop.
There may also be:
- extreme abdominal pain.
Anyone who believes they have been bitten by a black widow spider, and who is experiencing severe pain and stiffness near the area of the bite, should seek emergency care.
Depending on the severity of the reaction to the venom, doctors may decide to use antivenom to treat the bite.
The following spiders are common in the U.S.:
Black widows are found throughout the U.S. and are most common in warm, dry areas. A black widow bite will often show fang marks and a person may experience swelling, muscle aches, and cramps in the areas surrounding the bite.
Brown widows are prominent in southern California and are often found in buildings, cars, and vegetation. They are generally less aggressive than black widows but their venom is stronger. Brown widow bites are relatively harmless.
Funnel-web spiders have distinctive funnel-shaped webs that make them easy to identify. They are found throughout North America and are one of the deadliest spiders in the world. An antidote is available but needs to be administered almost immediately.
Wolf spider (Lycosidae)
The wolf spider is common all over the United States and is unique for not weaving webs. They are large and hairy, and people often mistake them for tarantulas. Wolf spider bites are poisonous and often very painful, but they are not lethal.
Yellow sac (Cheiracanthium inclusum)
Yellow sac spiders are found throughout the U.S., often indoors. Redness and swelling are the most common symptoms of a yellow sac bite.
Brown recluse spider
The brown recluse spider is most commonly found in the darkest parts of a house. It is attracted to warm and dry climates and is found primarily in the south and central areas of the United States. Brown recluse spider bites are usually minor but can cause hemolysis, or the rupturing of red blood cells, in rare cases.
The hobo spider was first discovered in Europe and can be found in various North American states. It is most commonly found in tight spaces and cracks, both inside and outside. A person with a hobo spider bite will often experience redness and swelling in the affected area.
Camel spiders are desert creatures that people often mistake for scorpions. In the United States, they are most common in southwest deserts. While painful, their bites are not deadly to humans.
Insect bites can have different effects.
The effects of a tick bite normally disappear within 3 weeks, but if mouth parts remain on the skin, signs and symptoms can persist. Ticks commonly occur in long grass and where deer live.
Tick bites are not generally painful, but a lump may develop. However, ticks can cause Lyme disease, Rocky Mountain spotted fever, ehrlichiosis, and babesiosis, among others. These common conditions can be serious.
Midges, mosquitoes, and gnats
Bites normally cause small, itchy lumps, or papules. Blisters or weals may develop in sensitive individuals.
A flea bite typically leads to a wheal that normally peaks in 5 to 30 minutes, and then becomes a hardened papular lesion within 12 to 24 hours. Sensitive people may find the site will itch for a week or more.
Fleas can transmit diseases such as typhus and Yersinia pestis (Y. pestis), commonly known as plague.
Horseflies can deliver a painful bite. This may be accompanied by:
- eyes and lips may be itchy, with pink or red swellings
- general weakness
- hives (urticaria, a rash of wheals)
Horsefly bites may take a long time to heal, because the insect cuts into the skin when it bites.
Initial bedbug bites do not generally cause a reaction, but sensitized individuals may develop weals or papules after a subsequent bite. Find out more about bedbugs.
Bed bugs constitute a major public health problem.
Getting rid of bed bugs includes throwing away the mattress and washing sheets and clothes in very hot water.
Sand flies are very small flies that occur mostly in tropical and subtropical areas, from the rain forests of Brazil to the deserts of Western Asia.
They are around 3 millimeters long and gold, brown, or grey in color.
In the past, they were uncommon in the U.S., but they may occur in the southern states. In 2012, they were reported in Kansas and Missouri. They favor hardwood forests and tend to bite from dawn to dusk.
People may also be affected while travelling or serving overseas in a military capacity.
The bite of the sandfly can be painful and itchy. Red bumps and blisters may develop. Sometimes, ulceration may result.
The fly can also transmit diseases, such as leishmaniasis and the Heartland virus. Leishmaniasis is a serious disease that can result in skin sores, a fever, and a low white blood count, depending on the type of leishmaniaisis.
The Heartland virus is another serious infection that normally requires hospitalization.
The following images show what can happen with some types of bite. However, the effects may differ between individuals.
A bite from a tick with Lyme disease often leaves a bullseye pattern.
Mosquito bites can be itchy. They can become infected through scratching.
Flea bites may itch for a week or more.
A horsefly bite can take time to heal, as the insect cuts into the skin. Image credit: Citron, 2011
Bed bug bites can form a distinctive pattern.
Brown recluse spider
The impact of a brown recluse spider bite can seem small at first, but it last for several months.
Sandfly bites can spread leishmaniasis and other diseases.
The likelihood of receiving an insect bite depends on the environment.
Common sources of fleabites include pets, crowded communities with low hygiene standards, and birds' nests. Moving into a new home that has been empty for a while can activate dormant fleas.
Bedbugs favor old properties and upholstery. They commonly occur in low-income rental properties and hotels. They live in mattresses, clothing, and so on.
Some people are more prone to bites from ticks and mice because of their occupation.
Traveling and camping can increase the risk of insect bites.
Insect bites are normally easy to diagnose, but a person will only contact the doctor if there is a severe reaction.
If symptoms persist or are severe, it is a good idea to see a dermatologist.
A mild and limited reaction normally passes within a few days. A cold compress on the affected area, oral painkillers, a steroid cream, or anesthetic cream may soothe the discomfort. Antihistamine sometimes helps. A variety of bite treatments are available to purchase over the counter or online.
A more serious local reaction may require oral antihistamines or oral analgesic.
In more severe cases of swelling, the doctor may prescribe oral steroids.
Small, itchy lumps or lesions near bite can be treated with an oral corticosteroid, such as prednisolone, or an oral antihistamine.
Scratching the skin or bursting a blister can enable bacteria to enter and cause an infection.
If there are large skin reactions and more generalized symptoms, the doctor may refer the patient to a specialist for desensitization, or treatment for an allergic reaction.
If symptoms worsen or do not improve, medical attention should be sought.
If bites are from fleas, mites or bedbugs, the patient should try to find where the infestation is. If it comes from a pet, the pet will need treating, as well as its bedding, soft furnishings, and carpets throughout the house.
Bedbugs will mean calling pest control company to come and decontaminate the home. To prevent bedbugs, bedding should be washed often at a high temperature, and old pillows and mattresses replaced.
The tick must be removed immediately, to lower the risk of an infection, such as Lyme disease.
The best way is to hold the tick as close to the skin as possible, preferably with a pair of tweezers, and pull it straight up, making sure all its parts are removed.
Twisting or jerking it are not advised, as this can break it, leaving bits behind in the skin. Petroleum jelly, alcohol, or a lit match are not effective.
The hands and the bite area should be washed with soap and water after removing the tick, and an antiseptic applied.
Scratching increases the chance of swelling, and it raises the risk of infection. Most tick bites will heal within 2 to 3 weeks.
If a rash develops around the armpit, thighs or groin, or if there are flu-like symptoms, it is important to seek medical attention. The doctor will probably prescribe antibiotics to prevent Lyme disease.
Some ticks carry diseases, such as Rocky Mountain spotted fever and Lyme disease.
Lyme disease is caused by Borrelia burgdorferi, a bacterium that some ticks carry. The patient develops a red rash that spreads outwards. Lyme disease can be treated with antibiotics.
Different types of mosquito transmit different diseases, for example, West Nile virus and malaria.
To prevent insect bites, especially in warm weather, the following steps may help:
- Using structural barriers, such as window screens or netting
- Avoiding wooded, brushy and grassy areas
- Avoiding heavily scented cosmetics and bright colored clothing
- Covering drinks and garbage cans
- Wearing long sleeves and long pants, tucked into shoes or socks, and a hat
- Checking containers for stagnant water, as this provides a breeding ground for mosquitoes.
It may be necessary to use an insect repellent. The active ingredient should be approved by the Environmental Protection Agency (EPA). It can be sprayed onto clothes and skin, but not the face. It is important to follow the product's instructions carefully.
Insect repellent is not suitable for infants. If a child is less than 10 years old, the repellent should contain no more than 10 percent DEET. Oil of eucalyptus can be effective, but it is not suitable for children under 3 years old.
Insect repellants are available to purchase online. Check that it contains a maximum of 10 percent DEET if it is to be used for children.
Repellent should not be applied to children's hands, around the eyes, or to areas where there are cuts and irritated skin.
When using an insect repellent and a sunscreen, the sunscreen should be applied first.
Clothes, shoes, and camping gear can be purchased or treated with permethrin. Permathrin spray is available for purchase online. Tents should be pitched away from water or swamps.
Travelers should check whether the area they are going to has a risk of infection, and take the necessary precautions.
Local health departments and park authorities can provide information about tick-infested areas. If it is not possible to avoid a tick-infested area, it is best to walk in the center of paths, to avoid contact with vegetation.