September 20, 2004

Experts from several agencies have investigated and believe they have identified the culprit in a recent round of mysterious insect bites in the Lincoln, Neb., area. It appears that most of the bites are from a Pyemotes mite, a tiny arthropod commonly called an itch mite.

Mystery bites have been reported by young and old. People who spend time outdoors have been most likely to be bitten, but those who remain indoors most of the time also are bitten occasionally. The bites don't hurt when they occur, but one or more red spots later appear on the limbs, neck and torso. Unlike chigger bites, these mystery bites are not confined to ankles, feet, legs and the belt line. Some bites are quite small, but some may be as large as a quarter and each has a raised center which may take the form of a small watery blister. The bites may occur in clusters, forming a rash which may last for several days.

With most people there are no apparent secondary effects, however some have reported headache, fever, nausea or asthmatic symptoms. The bites are intensely itchy, but scratching provides little relief and seems to increase pain and tenderness. No one is seeing insects or associating them with these lesions, but several have reported that they were working outdoors, and often standing in the shade of pin oak trees.

The culprit, a microscopic Pyemotes mite, is in the area preying on small fly maggots that cause the "leaf edge" galls on pin oak leaves. The galls are unusually abundant this year. In many cases, the maggots that caused the galls have matured and are emerging in the millions and dropping to the ground. These are harmless. However, in examining empty galls, in which one or more maggots were killed, large numbers of the itch mites, a predator of the maggots, were found. This observation is being confirmed by entomologists at the University of Nebraska-Lincoln and at Kansas State University.

These microscopic mites, carried by the wind, are tiny enough to penetrate the mesh of a standard window screen and may be overlooked because of their very small size. People sleeping with windows open could easily be bitten at night, giving the impression that something is infesting the bedroom. Yellow sticky traps placed in the vicinity of infested pin oak trees confirm that these mites are airborne and may number in the millions. We believe that the current emergence and period of biting activity should soon be over.

Other types of bites are also appearing at this time, which confuses the issue. Here are some bite descriptions, several of which are paraphrased from the text by Dr. Jerome Goddard, Physician's Guide to Arthropods of Medical Importance (1993), CRC Press. Symptoms and bite reactions may vary somewhat due the sensitivity of different individuals.

Bite Descriptions:

Pyemotes (itch) mites: No pain on the initial bite. Ultimately a red spot appears, which may vary in size from 1/4- to 1-inch in diameter. In the middle of the red spot is a small, raised "pimple" or blister. The bites itch, but scratching provides little relief and aggravates the symptoms. Most bites occur on upper torso, the abdomen, back and neck, shoulders, and arms. Sensitive individuals may experience headache, fever, nausea, or asthmatic symptoms.

Mosquitoes and "No-See-Ums": Produce welts and itching, usually within 30 minutes of the bite. Reaction varies with sensitivity of the individual. Usually a persistent papular lesion. Mosquitoes are active and will continue until frost.

Chiggers (mites): Active and common, in lawns, pastures, roadside ditches, and brushy areas. These are parasitic on rodents. Cause intense itching, forming pustules and wheals, often with a central vesicle. Lesions occur within 3 - 6 hours of exposure. Bites occur mainly on lower half of the body, especially where clothing binds somewhat -- the tops of socks, underwear elastic and the beltline.

Fleas: Usually associated with cats or dogs, reaching peak numbers in August and September. Bites have a central spot surrounded by a reddish ring. Cause pain while feeding. Little swelling, but center may raise up to form a vesicle. Lesions may appear in groups, often secondarily infected.

Black Fly: Active where there is relatively clean, well-aerated, running water, including both natural and artificial streams. Larvae attach to rocks, stones and other submerged surfaces. Bites are painful and consist of reddened, itching papules on the head and neck, especially at the base of the head. Considerable swelling. Attack arms, legs and face, but often concentrate on neck. Often feed beneath clothing and sometimes leave a blood spot at the feeding site.

Pirate Bug: A small (1/16-inch long) black and white sucking insect that is mostly beneficial, since it feeds on aphids and mites that attack crop plantings. Being vicious predators, they often attempt to bite humans as well. The bite is very painful and itches for some time after.

Other pests can also bite, but these are large enough to see and to associate with the biting activity. These include certain spiders, lace bugs, which feed on oak trees; damsel bugs, another useful predator insect; and the lady beetle known as the Halloween Beetle (Harmonia sp.).

What to Do?
Our best advice is the following:

1. Limit outdoor activity until the problem subsides, we estimate this should occur within the next 7 - 10 days.

2. When you come back indoors, be sure to take a hot shower, lathering generously.

3. Launder clothing after wearing -- don't reuse yesterdays shirt.

4. As a general treatment for biting insects and mites, we usually suggest calamine lotion, antihistamine cream, such as Benadryl, or hydrocortisone cream, any of which should reduce itching. Wash the site often with soap and use an appropriate antiseptic and antibiotic ointment to keep wound clean and to promote healing. Don't scratch.

Investigation Team: Agencies working together on this problem are: the University of Nebraska-Lincoln Department of Entomology, the Nebraska Department of Health and Human Services, Lancaster County Health Department, The U.S. Department of Agriculture's Agricultural Research Service and entomologists at Kansas State University who are in turn collaborating with the Centers for Disease Control in Atlanta.

9/20/04

David Keith - Ph.D.
Entomology
Professor
(402) 472-8918

Fred Baxendale - Ph.D.
Entomology
Professor
(402) 472-8699

James Kalisch
Entomology
Extension Technologist
(402) 472-8691

Sandi Alswager Karstens
IANR News and Photography
(402) 472-3030

Department: Entomology