Insect bites: Reactions, types, and images

Insect bites are puncture wounds or lacerations made by insects. An insect may bite when it is agitated and defends itself, or when it wants to feed.

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.

Fast facts about insect and spider bites

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.
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.

In colder climates, the risk of catching diseases from insect bites is small. However, nearer the equator 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 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.

Spider bites

[brown recluse spider]
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.

black widow spider bite
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 widow

brown widow spider 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 (Dipluridae)

funnel-web spider bites
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)

wolf spider bites
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 spider bites
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

brown recluse spider bites
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.

Hobo spider

hobo spider bites
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 spider

camel spider bites
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

Insect bites can have different effects.

Tick bites

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.

Mosquito bites can transfer diseases, such as malaria, Zika, dengue fever, yellow fever, and encephalitis.


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.

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