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.
In this article, we look at the types of insect that bite, how people react, and how to manage a bite.
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, sand flies are among the insects that bite. Spiders are not strictly insects but can also bite.
Individuals react in different ways. In one person, a bite might cause a small, itchy lump that resolves in a few days. In another, the same bite can have a more serious effect.
Infection might occur at the site of a bite, causing redness, warmth, and a hardening of the skin around the area, with pus draining from the wound.
Scratching the wound can also lead to infection and leathery, thick skin. This process is called "lichenification."
People who work outdoors or regularly participate in outdoor activities are more at risk of insect bites.
In colder climates, the risk of catching diseases from insect bites is low. However, nearer the equator, temperatures are much higher. Here, insect bites can lead to malaria, sleeping sickness, dengue fever, or the Zika virus.
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 fill with fluid. Inflammation sometimes occurs around the area around the lump.
Insect bites normally disappear within a few days without any need for medical attention.
Some people have an allergic reaction to insect bites. However, bites rarely cause a severe allergic reaction, unlike insect stings.
The following may indicate a severe allergic reaction:
- an often blotchy rash can spread to other parts of the body
- breathing difficulties
- chest pain
- faintness or dizziness
- rapid heartbeat
- severe swelling, which might occur in a body part some way 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 a particular type of insect bites them. The individual might have experienced sensitization, in which an individual becomes more sensitive to the insect's saliva.
An insect bite that develops infection 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 receiving a number of bites.
Allergic reactions to insect bites 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 and do bite. Some spider bites are quite dangerous to humans.
The bite of the brown recluse, for example, produces only a mild sting at the time of the bite. However, it can be very damaging, causing tissue destruction and severe pain.
Redness develops in the bite area. 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 resolves without any further problems. However, on other occasions, this ulceration spreads, or bacteria superinfect the ulcer.
Symptoms include a mild fever, listlessness, nausea, and, sometimes, a rash. Death is rare but possible, especially in small children. Seek medical attention after recent contact with a brown recluse if a spreading ulceration or redness and infection occur.
The black widow is the most venomous spider in the U.S., but its bite is rarely deadly. The bite feels like a pinprick in the skin. A slight swelling and faded red marks might develop, but, within a few hours, stiffness and extreme pain may come on.
A person might also experience:
- 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 occur 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 common 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 an individual needs a dose almost immediately after the bite.
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. However, they are not lethal.
Yellow sac (Cheiracanthium inclusum)
Yellow sac spiders occur 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 most commonly inhabits the darkest parts of a house. Warm and dry climates attract it, so they occur mainly 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 first emerged in Europe and now inhabits various North American states. It is most common 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 resolve within 3 weeks, but if mouth parts remain on the skin, symptoms might persist. Ticks commonly occur in long grass and around deer habitats.
Tick bites are not generally painful, but a lump may develop. However, ticks can cause Lyme disease, Rocky Mountain spotted fever (RMSF), ehrlichiosis, and babesiosis, among others. These conditions can cause serious health problems.
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 peaks in 5 to 30 minutes and then becomes a hardened papular lesion within 12–24 hours. People who are sensitive to insect bites might experience itching around the site for a week or more.
Fleas can transmit diseases, such as typhus and Yersinia pestis (Y. pestis), or the plague.
Horseflies can deliver a painful bite. The following symptoms might accompany a horsefly bite:
- possible itchiness of the eyes and lips, with pink or red swellings
- general weakness
- hives, or 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 individuals with high sensitivity may develop weals or papules after a subsequent bite. Find out more about bedbugs.
Bed bugs are 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 rainforests of Brazil to the deserts of Western Asia.
They are around 3 millimeters (mm) long and gold, brown, or grey in color.
In the past, they were uncommon in the U.S., but they now might occur in the southern states. In 2012, people reported sandflies in Kansas and Missouri. They favor hardwood forests and tend to bite from dawn to dusk.
People may also receive sandfly bites while traveling 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 might 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.
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. Infection occurs 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 lasts for several months.
Sandfly bites can spread leishmaniasis and other diseases.
The risk 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 also increase the risk of insect bites.
Insect bites are normally easy to diagnose, but a person will only contact the doctor in cases that involve 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 (OTC) or online.
A more serious local allergic reaction may require oral antihistamines or oral painkillers.
In more severe cases of swelling, the doctor may prescribe oral steroids.
A person can treat small, itchy lumps or lesions near a bite with an oral corticosteroid, such as prednisolone, or an oral antihistamine.
Scratching the skin or bursting a blister might allow bacteria to enter and cause an infection.
If severe reactions in the skin and more generalized symptoms occur, the doctor may refer the individual to a specialist for desensitization, or treatment for an allergic reaction.
If symptoms get worse or do not improve, seek medical attention.
If bites come from fleas, mites, or bedbugs, try to find the source of the infestation. If these insects come from a pet, the pet will need treatment, as well as its bedding, soft furnishings, and carpets throughout the house.
Bedbugs will mean calling out a pest control company to decontaminate the home. To prevent bedbugs, wash bedding at a high temperature, and replace old pillows and mattresses.
Remove the tick immediately to reduce 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 upward, being sure all its parts.
Do not twist or jerk the tick, as this can break it, leaving parts behind in the skin. Petroleum jelly, alcohol, or a lit match are also not effective.
Wash the hands and the bite area with soap and water after removing the tick, and apply an antiseptic.
Scratching increases the chance of swelling and increases the risk of infection. Most tick bites heal within 2 to 3 weeks.
If a rash develops around the armpit, thighs, or groin, or an individual experiences flu-like symptoms after a tick bite, seek medical attention. The doctor will probably prescribe antibiotics to prevent Lyme disease.
Some ticks carry diseases, such as RMSF and Lyme disease.
Borrelia burgdorferi, a bacterium that some ticks carry, causes Lyme disease. The individual develops a red rash that spreads outwards. Antibiotics can also help treat Lyme disease.
Different types of mosquito transmit different diseases, such as 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, tucking these into shoes or socks, and wearing a hat
- checking containers for stagnant water, as this provides a breeding ground for mosquitoes.
Using an insect repellent may be necessary. The Environmental Protection Agency (EPA) should have issued approval for the active ingredient in the spray. A person can spray repellent onto their clothes but should avoid the face. Follow the product's instructions carefully.
Insect repellent is not suitable for infants. If a child is under 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 of age.
Insect repellents are available to purchase online. Check that it contains a maximum of 10 percent DEET if it is to be used for children.
Do not apply repellent to children's hands, areas around the eyes, or to cuts and irritated skin.
When using an insect repellent and a sunscreen, apply the sunscreen first.
A person can buy clothes, shoes, and camping gear to which manufacturers have added permethrin. Permethrin spray is available for purchase online. Pitch tents away from water or swamps.
Travelers should check whether the area they are visiting has a risk of infection and take the necessary precautions.
Local health departments and park authorities can provide information about tick-infested areas. If a person cannot avoid a tick-infested area, they should walk in the center of paths to avoid contact with vegetation.