Bed bugs bites can leave a colorless welt along with an itching or burning sensation. (Image courtesy of the Centers for Disease Control and Prevention.)

This is a black widow spider. Note the red "hour glass" on the abdomen. The bite of the black widow can produce severe symptoms but is seldom fatal, except in young children and older adults. (Image courtesy of the Centers for Disease Control and Prevention.)

This is a magnified view of a body louse. Lice produce itching and a characteristic skin rash, which looks like a scrape. Lice may also carry organisms that cause relapsing fever, typhus, and trench fever. (Image courtesy of the Centers for Disease Control and Prevention.)

Different types of fleas prefer specific animals as hosts, but will infest humans if their specific hosts are unavailable. Fleas can carry plague and typhus. They are also thought to transmit several other diseases. (Image courtesy of the Centers for Disease Control and Prevention.)

Flies carry disease by transporting infectious agents on their feet. They may spread salmonellosis, typhoid, and other diseases. (Image courtesy of the Centers for Disease Control and Prevention.)

Triatomid, the kissing bug, can carry Chagas' disease (American trypanosomiasis). (Image courtesy of the Centers for Disease Control and Prevention.)

This is a magnified photograph of a dust mite. Mites are carriers (vectors) of many important diseases including typhus (scrub and murine) and rickettsialpox. (Image courtesy of the Centers for Disease Control and Prevention.)

There are many different species of mosquito, which can carry some of the world's most common and significant infectious diseases, including West Nile, Malaria, yellow fever, viral encephalitis, and dengue fever. (Image courtesy of the Centers for Disease Control and Prevention.)

Wasps are not known to carry human diseases, but allergic reactions to their sting can be fatal. (Image courtesy of the Centers for Disease Control and Prevention.)

Allergic reaction to bee stings occurs when a person becomes sensitized to the venom from a previous sting. This reaction is different from the reaction to the poison in the bite of a black widow spider, which injects a potent toxin into the blood. Ordinarily, bee venom is not toxic and will only cause local pain and swelling. The allergic reaction comes when the immune system is oversensitized to the venom and produces antibodies to it. Histamines and other substances are released into the bloodstream, causing blood vessels to dilate and tissues to swell. Severe reactions can lead to anaphylactic shock, a life-threatening series of symptoms including swelling of the throat and difficulty breathing. Persons who develop an allergy to bee stings should carry prescription bee sting kits to counteract the reaction to bee venom.

The brown recluse is a poisonous spider most commonly found in midwestern and southern states of the United States. It is about one-half inch overall and has long skinny legs. The brown recluse is brown with a characteristic dark violin-shaped marking on its head. It is most commonly found outside in wood, leaves, or in piles of rocks. If a brown recluse wanders indoors they will go to dark closets, shoes, or attics. The brown recluse is a non-aggressive spider and will only bite when it is disturbed.

The female black widow is easily recognized by her shiny black body and red hourglass marking underneath her round abdomen. Although black widows can be found in nearly every state they are most common in the southern areas of the United States. The black widow makes her home in wood piles, under eaves, and other undisturbed places. The bite of a black widow can be serious and require medical attention. Symptoms include pain radiating from the site of the bite, nausea, overall aching of the body, profuse sweating, and labored breathing.

To remove a stinger, scrape the back of a knife or other straight-edged object across the stinger. Do not use tweezers since it may squeeze the venom sac and increase the amount of venom released into the wound. Next wash the site thoroughly with soap and water. Place ice wrapped in a washcloth or other suitable covering on the site of the sting for 10 minutes and then off for 10 minutes. If needed an antihistamine can be applied to help reduce the itching. Over the next several days the stinger site should be watched for signs of infection, such as increased redness, swelling, or pain.

Fleas are blood-feeding insects. Pain and itching results from an allergic reaction to the materials that the fleas inject into the skin at the time of the bite.

This is a 2 to 3 centimeter wide blood-filled (hemorrhagic) blister (bullae) that has resulted from an insect bite. It is located on the wrist. Bullae formation and tissue necrosis (death) are more common with spider bites, but may also be caused by insect bites.

Insect bites may be grouped, raised (papular), hive-like (urticarial) and have a surrounding halo. Occasionally a central depression, or punctum, can be seen.

This is a photograph of a male Pediculus humanus var. capitis, a head louse. Head lice have become an increasing problem in schools and day care centers. Some grade schools have started programs to examine children for head lice.

This is a photograph of a female Pediculus humanus var. capitis, a head louse. Head lice have become an increasing problem in schools and day care centers. Some grade schools have started programs to examine children for head lice.

This is a close-up picture of lice egg sacks (nits) on the hair. They cling to individual hair shafts. (Image courtesy of the Centers for Disease Control and Prevention.)

These are Pediculus humanus, or body lice. Other types of lice infest the scalp, head (Pediculus humanus capitis), or the pubic area (Phthirus pubis). Some body lice may carry diseases such as epidemic typhus, relapsing fever, or trench fever. (Image courtesy of the Centers for Disease Control and Prevention.)

This is a magnified view of a female body louse with larvae. Lice cause itching and a characteristic excoriated skin rash (looks like a scrape). They may also transmit diseases, including relapsing fever, typhus, and trench fever. (Image courtesy of the Centers for Disease Control and Prevention.)

This is a photomicrograph of a female pubic louse. The condition known as "crabs" is so named because of the resemblance of a pubic louse to a crab. The bodies of pubic lice are shorter and rounder than those of head lice. (Image courtesy of the Centers for Disease Control and Prevention.)

This is a photomicrograph of a male pubic louse. The condition known as "crabs" is so named because of the resemblance of a pubic louse to a crab. The bodies of pubic lice are shorter and rounder than those of head lice.

This picture compares the relative size and shape of the head louse and the pubic louse.

This lesion was produced by the bite of a brown recluse spider. The brown recluse is one of two common spiders in the United States considered poisonous. (The other is the black widow.) However, the hobo spider, wolf spider, and jumping spider can also produce bites that require medical attention.

Even though some insect bites or stings can be extremely painful they usually do not require emergency medical care. Although the stung or bitten area should be carefully observed for signs of infection or reaction to venom.