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Symptoms and Signs of Insect Bites

Doctor's Notes on Insect Bites

Insects are small animal arthropods that have six legs (hexapod invertebrates) and generally one or two pairs of wings. There are an estimated 10 million different insect species. However, the lay press equates insects with almost any small bug or animal that bites or stings. Consequently, insect bites may be attributed to not only small arthropods but to other small invertebrate animals that can either bite, sting or cause a chemical reaction (for example, blisters or pain) in human skin. Although some individuals would exclude stinging from biting insects, most medical and/or nonmedical individuals include stinging animals when discussing insect bites.

The causes of insect bites are numerous and although most insect bites are caused by true insects, some are not. The major causes of insect bites and stings in the US are as follows: mosquito bites, fire ant stings, bee stings, wasp stings, flea bites, chigger bites, tick bites, brown recluse spider bites, black widow spider bites, reduviid bug (also termed kissing bugs or Triatomine bugs) bites, puss caterpillar (skin reaction to released chemical skin irritant), and blister beetle (skin reaction to released chemical skin irritant)

If you can safely capture the insect or bug that likely bit or stung you, this may help your doctor to design the best treatment, if any, for you. However, if you develop any problems like tissue swelling or shortness of breath, go immediately to the emergency department.

Although many insect bites, stings and released chemicals result in reddish itchy skin, some have signs and symptoms that may help identify the cause. The following are: mosquito bites; reddish raised itchy, lesions, Fire ant stings produces blisters that are small and have pus in the center of the blister, bee stings with painful welt with possible mark in the center where the bee stung, wasp stings similar to bee sting, Flea bites with small red bumps that itch, mainly on the legs and ankles, chigger bites with small red lesions usually in warm areas like the waist, elbow and knee folds, tick bites after or during the initial bite - the initial bite site may be reddish, brown recluse spider bites begins as reddish skin that can develop into a skin ulcer, black widow spider bites; begin as two red puncture marks and can ulcerate, reduviid bug bites get contaminated with bug’s feces; reddish-brown skin rash, puss caterpillar (skin reaction to released chemical skin irritant); 2-4 rows of painful, reddish, small lesions that mimic the shape of the caterpillar, and blister beetle (skin reaction to released chemical skin irritant when bug is crushed); painful skin blisters, some lesions.

Although most insect bites signs and symptoms usually only last a few days, many insects are vectors that may carry viruses, bacteria and parasites that can harm humans or even kill them. Mosquitos can be vectors of several diseases that include malaria, yellow fever, West Nile, Dengue, elephantiasis and Zika virus. Depending on the type of tick, Lyme disease (signs and symptoms of reddish target lesions or Rocky Mountain spotted fever (symptoms include small reddish rash) can be transmitted to humans. Reduviid bug bites can transmit the parasites that cause Chagas disease with symptoms that include fever, eyelid swelling, headache and splenomegaly. Stings from such insects as bees, wasps and other flying insects that bite can cause allergic reactions that can be life-threatening such as swelling of the tongue or throat that can stop breathing if not treated emergently. Some skin lesions produced by insect bites may become infected. Brown recluse spider bites can result in local tissue destruction and crater-like scarring while the black widow spider bites can cause severe muscle cramping and central nervous system excitation due to the neurotropic toxin released in the bite.

Medical Author:
Medically Reviewed on 3/11/2019

Insect Bites Symptoms

The response to a sting or bite from insects or "bugs" is variable and depends on a variety of factors. Most bites and stings result in: 

  • pain,
  • swelling,
  • redness,
  • itching, or
  • blister.

The skin may be broken and become infected. If not treated properly, these local infections may become severe and cause a condition known as cellulitis.

  • You may experience a severe reaction beyond the immediate area of the sting if you are allergic to the bite or sting. This is known as anaphylaxis.
  • Symptoms of a severe reaction include:
    • hives,
    • wheezing,
    • shortness of breath,
    • unconsciousness, and even
    • death within 30 minutes.
  • Stings from large hornets or multiple (hundreds or thousands) bee stings have been reported to cause muscle breakdown and kidney failure and death.
  • Bites from a fire ant typically produce a pustule, or a pimple-like sore, that is extremely itchy and painful.
  • Spider bites like the brown recluse may cause blistering and necrotic skin ulceration while black widow spider bites cause more systemic symptoms such as:
  • Ant bites are usually seen singly or in small clusters and each bite may develop a small central area of pus.

In the past few years, researchers have found that tick bites (from the lone star tick) can generate an allergic response to red meat (beef, pork and venison, for example) and even milk.

These problems may occur from the bite and the antigens that accompany the saliva during the bite or sting. The added problems of pathogen transfer during the bite, sting or feeding process are detailed in separate articles and will only be mentioned briefly in this general article.

Insect Bites Causes

Most insects do not usually attack humans unless they are provoked. Many bites and stings are defensive. Insects sting to protect their hives or nests or when incidentally touched or disturbed (so hives and nests should not be disturbed or approached).

A sting or bite injects venom composed of proteins and other substances that may trigger an allergic reaction in the victim. The sting also causes redness and swelling at the site of the sting.

Bees, wasps, hornets, yellow jackets, and fire ants are members of the Hymenoptera family. Bites or stings from these species may cause serious reactions in people who are allergic to them. Death from bee stings is 3 to 4 times more common than death from snake bites. Bees, wasps, and fire ants differ in how they inflict injury.

  • When a bee stings, it loses the entire injection apparatus (stinger) and actually dies in the process.
  • A wasp can inflict multiple stings because it does not lose its injection apparatus after it stings.
  • Fire ants inject their venom by using their mandibles (the biting parts of their jaw) and rotating their bodies. They may inject venom many times.
  • Puss caterpillars (Megalopyge opercularis or asp) have hollow "hairs" or spines (setae) that break when touched and toxin is injected into the skin.
  • In contrast, bites from mosquitoes are not defensive; mosquitoes are looking to get blood for a meal.
    • Typically, most mosquitoes do not cause significant illnesses or allergic reactions unless they convey "vectors," or pathogenic microorganisms that actually live within the mosquitoes. For instance: 
      • malaria is caused by an organism that spends part of its life cycle in a particular species of mosquitoes.
      • West Nile virus is another disease spread by a mosquito. Various mosquitoes spread other viral diseases such as
      • equine encephalitis;
      • Zika virus (suspected of causing microcephaly);
      • dengue; and
      • yellow fever to humans and other animals.

Other types of insects or bugs that bite for a blood meal and diseases that are possibly transmitted are as follows:

  • Lice bites can transmit epidemic relapsing fever, caused by spirochetes (bacteria).
  • Leishmaniasis, caused by the protozoan Leishmania, is carried by a sand fly bite.
  • Sleeping sickness in humans and a group of cattle diseases that are widespread in Africa, and known as, are caused by protozoan trypanosomes transmitted by the bites of tsetse flies.
  • Bacteria-caused diseases tularemia can be spread by deer fly bites, the bubonic plague by fleas, and the epidemic typhus rickettsia by lice.
  • Ticks (arachnids) can transmit Lyme disease and several other illnesses through their bites; ticks bite so they can obtain a blood meal.
  • Other arachnids (bugs) such as chiggers, bedbugs, and mites typically cause self-limited localized itchiness and occasional swelling.
  • Serious bites from spiders (arachnids), which are not insects, can be from the black widow or brown recluse spiders; the spiders bite usually as a defense mechanism.

Other insects and bugs can transmit diseases by simply transferring pathogens like Salmonella spp by contact. For example, in unsanitary conditions, the common housefly can play an incidental role in the spread of human intestinal infections (such as typhoid, bacillary and amebic dysentery) by contamination of human food as it lands and "walks" over foods after previously "walking" on contaminated items like feces.

Bad Bugs Identify Bug Bites From Mosquitos, Spiders and More Slideshow

Bad Bugs Identify Bug Bites From Mosquitos, Spiders and More Slideshow

Ticks are often found in plants and brush, and can attach to and bite people and animals. Most tick bites are not harmful; however, ticks can carry serious diseases including Lyme disease and Rocky Mountain spotted fever.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.