by Nina Bicknese, Natural History Biologist   also: Chiggers pdf

image of chigger
Enlarged approximately 1,500 times, this chigger looks like the latest sci-fi movie star. In life, chiggers are red, but not from dining on blood as many people think. The larval form of a type of mite, chiggers are barely visible to the naked eye.

Courtesy Dr. W. Calvin Webourn and the Ohio State University Acarology Laboratory.

THE WORST THING about the Missouri summer isn't sunburn, heat or humidity-it's chiggers.

Chiggers first show up as annoying red bumps. An itch begins. It grows. More hard red welts surface. From your feet and ankles upward, and especially at those tender locations your mother told not to scratch in public, a maddening itch takes hold.

Savage scratching begins. Every welt becomes a persistent, exquisitely itching preoccupation that continues to irritate for days and even weeks. You probably recognize these symptoms of chigger bites. Yet we never see the culprits responsible for this summertime agony. What are chiggers? Why do they bite us? How can we stop that horrible itching?

Myths about chiggers are widespread. Many believe chiggers are some type of bug. Folklore tells us they burrow under our skin and die, that they drink our blood and that they can best be killed by suffocation with nail polish or bathing with bleach, alcohol, turpentine or salt water. Surprisingly, all these popular facts are just plain wrong.

Chiggers are not bugs or any other type of insect. Chiggers are the juvenile (or larval) form of a specific family of mites, the Trombiculidae. Mites are arachnids, like spider and scorpions, and are closely related to ticks.

Chigger mites are unique among the many mite families in that only the larval stage feeds on vertebrate animals; chiggers dine on us only in their childhood, and later become vegetarians that live on the soil.

Chiggers are tiny-less than 1/150th of an inch in diameter. More than a thousand of them could line up across this page and still leave room for two or three hundred more. At this size, chiggers are almost invisible to the unaided eye. However, when several chiggers cluster together near an elastic waistband or wrist watch they can be seen because of their bright red color.

Chiggers are born red; they do not become red from feeding on blood as some believe. An engorged, well-fed chigger changes to a yellow color.

Under the microscope, you can see that the chigger is an ugly little creature (if it was larger, it could star in any science fiction movie). Although adult chigger mites have eight legs, the troublesome young chiggers has only six.

One of the greatest misconceptions about chiggers is that they burrow into our skin and eventually die within the tissues, thus causing the persistent itch. This widespread myth has its origin in the southern states where pests with similar names such as jigger flea or the chigoe do attack by burrowing under skin. Chiggers are not equipped to burrow, and they are much too large to enter through the pores.

If chiggers do not burrow under skin or drink blood, what are they doing that itches so much? Chiggers do bite us, much like ticks do. Chiggers attach by inserting minute specialized mouth parts into skin depressions, usually at skin pores or hair follicles.

The chigger's piercing mouth parts are short and delicate, and can penetrate only thin skin or where the skin wrinkles and folds.

That's why most chigger bites are around the ankles, the back of the knees, about the crotch, under the belt line and in the armpits. The insertion of the mouth parts is not perceptible. The bite alone is not the source of the itch.

The reason the bite itches so intensely and for such a long time is because the chigger injects saliva into its victim after attaching to the skin. This saliva contains a powerful digestive enzyme that literally dissolves the skin cells it contacts. It is this liquefied tissue, never blood, that the chigger ingests and uses for food.

A chigger usually goes unnoticed for one to three hours after it starts feeding. During this period the chigger quietly injects its digestive saliva. After a few hours your skin reacts by hardening the cells on all sides of the saliva path, eventually forming a hard tube-like structure called a stylostome.

The stylostome walls off the corrosive saliva, but it also functions like a feeding tube for the hungry chigger. The chigger sits with its mouthparts attached to the stylostome, and like a person drinking a milk shake through a straw, it sucks up your liquefied tissue. Left undisturbed, the chigger continues alternately injecting saliva into the bite and sucking up liquid tissue.

It is the stylostome that irritates and inflames the surrounding tissue and causes the characteristic red welt and intense itch. The longer the chigger feeds, the deeper the stylostome grows, and the larger the welt will eventually become. The idea that the welt swells and eventually engulfs the feeding chiggers is also a myth. Many people have seen a small red dot inside a welt (usually under a water blister), but this is the stylostome tube and not a chigger body.

The time required for a chigger to complete its meal varies with the location of the bite, the host and the species. If undisturbed, chiggers commonly take three or four days, and sometimes longer, to eat their dinner. This is not surprising when you consider that this is the first and last meal of the young chigger's life.

On human hosts, however, chiggers seldom get the chance to finish a meal. The unlucky chigger that depends on a human for its once-in-a-lifetime dinner is almost sure to be accidentally brushed away or scratched off by the victim long before the meal is complete.

It may give you some consolation to know that when a chigger is removed before it has fully engorged, it cannot bite again and will eventually die. Seems only just, doesn't it?

Itching usually peaks a day or two after the bite occurs. This happens because the stylostome remains imbedded in your skin tissue long after the chigger is gone. Your skin continues the itch, allergic reaction to stylostome for many days. The stylostome is eventually absorbed by your body, a slow process that takes a weak to 10 days, or longer.

It is of little comfort to learn that North American chiggers only bite humans by accident. Although our chiggers can feed on most animals, they are really looking for reptiles and birds, their preferred hosts. The itching reaction human skin has to chigger bites occurs because we are not their correct hosts. Chiggers that specifically prey on humans in Asia and Pacific Islands cause no itching!

Unlike ticks, which quietly wait for hosts, chiggers run about almost constantly. Chiggers tend to move towards and onto any new object placed in their environment. You can test your lawn for the presence of chiggers by placing a black piece of cardboard or a white saucer. Vertically on the ground. If chiggers are present they will move rapidly over the object and accumulate on the upper edge where you can see them with a magnifying glass.

The chiggers that annoy people have long legs and can move rapidly. They are capable of getting all over a person's body in just a few minutes. The long trek from a victim's shoe to the belt line (a favorite point of attack) is a climb that take about 15 minutes but is more than 5000 times the chiggers's tiny length. That's about the same as a human scaling a large mountain-and on an empty stomach.

Chiggers are small enough to penetrate the meshes of your clothing, but they usually stay on the surface of your clothes until they come to an easy opening such as your cuffs, collar or waistband. Once they are on your body, chiggers wander about for an hour or more looking for a tender spot to dine. If these traveling chiggers reach an obstacle such as a belt or an elastic band, rather than cross over the obstacle or go under it, they stop and begin to feed.

The distribution of chiggers in any area is extremely spotty. Chiggers tend to congregate in patches, while nearby spots of apparently the same suitable living space is free of them. Often, people will be heavily attacked while sitting in a chigger concentration area, while the lucky folks sitting only a few yards away will get no bites at all.

Women and children get more bites than men. Folklore says that if chiggers have a choice, they will attack women before men. But the truth is that men, women and children collect the same number of chiggers during a walk in the woods. Women and children just have thinner skin, and thus more surface area that chiggers can easily bite.

Chiggers are affected by temperature. They are most active in afternoons, and when the ground temperature is between 77 and 86 degrees. Chiggers become completely inactive when substrate temperatures fall below 60 degrees; temperature below 42 degrees will kill the chigger species that bite us.

If you can, plan your outdoor activities around your thermometer reading to keep chigger bites to a minimum. Researchers have also found that chiggers actively avoid objects hotter than 99 degrees. Rocks that have been baking in the sun are almost always free of chiggers, and make a safe place to sit when you are in a chigger-infested area.

The first line of defense against chiggers is the right kind of clothing. Shorts, sleeveless shirts and sandals are nearly suicidal in chigger infested areas. Wear tightly woven socks and clothes, long pants long sleeved shirts, and high shoes or boots. Tucking pant legs inside boots and buttoning cuffs and collars as tightly as possible also helps keep the wandering chiggers on the outside of your clothes.

A chigger in relation to a human hair follicle. Chiggers do not burrow under the skin, but bite us, often at skin pores or hair follicles.

image of chigger in relation to human hair follicle
When you get home, change clothes as soon as possible, and wash them before you wear them again. If you don't, the chiggers will get you the next time you put them on.

Regular mosquitoes repellents will repel chiggers. All brands are equally effective. Applying these products to exposed skin and around the edge of openings in your clothes, such as cuffs, waistbands, shirt fronts and boot tops, will force chiggers to cross the treated line get inside your clothes.

Unfortunately these repellents are only potent for two to three hours and must be reapplied frequently.

By far, the most effective and time proven repellent for chiggers is sulphur. Chiggers hate sulphur and definitely avoid it. Powdered sulphur, called sublimed sulphur or flowers of sulfur, is available through most pharmacies. Dust the powdered sulphur around the opening of your pants, socks and boots. If you plan to venture into a heavily infested area, powdered sulphur can be rubbed over the skin on your legs, arms and waist. Some people rub on a mixture of half talcum powder and half sulphur.

But a word of warning: sulphur has a strong odor. The combination of sulfur and sweat will make you unpleasant company for anyone who has not had the same treatment. Sulphur is also irritating to the skin of some people. If you have not used sulphur before, try it on a small area of your skin first.

Some families have problems enjoying summer backyard activities because of chiggers. The most effective means to eliminate these chiggers is just remove the habitat favored by the adults and juveniles. Clearing away brush and weeds, keeping the grass cut close to the ground and removing conditions which attract small animals that cans serve as hosts is the best way to get chiggers out of your yard. Chiggers seldom survive in areas that are well groomed.

The best precaution against chigger bites is simply taking a warm soapy bath with plenty of scrubbing as soon as possible after exposure. If you bathe at once, while the chiggers are still running over your body, you can wash them off before they bite. A bath will also remove any attached and feeding chiggers before you start to feel the itch.

Warm soapy water is all that is necessary to remove and kill chiggers. There is no need, and it is rather dangerous, to apply household products such as kerosene, turpentine, ammonia, alcohol, gasoline, salt or dry cleaning fluid. Don't do it.

Attached chiggers are removed by even the lightest rubbing. If you are away from civilization, you can remove attached chiggers before they do much damage by frequently rubbing down with a towel or a cloth.

What can you do to alleviate suffering if these precautions fail? Lotions will relive the itching somewhat, but no substance is completely effective. The only ultimate cure is time, since there is nothing you can do to dislodge the chigger's feeding tube, the true cause of your itch. You must simply wait until your body breaks down and absorbs the foreign object.

In the meantime, local anesthetics such as benzocaine, camphor-phenol and ammonium hydroxide may provide you with several hours of comfort at a stretch. Over-the-counter creams can also help. In rare cases, some people are allergic to chigger bites and require prescription medications from their doctor.

The most popular home remedy for which there is little justification is to dab nail polish on the welt. This cannot "smother" the chigger because it has not burrowed into your skin, and it was probably scratched off long ago. The only benefit to applying a thick coat of nail polish is that it helps to remind you not to scratch the bite.

Chronic scratching will only cause the stylostome to further irritate. Scratching deep enough to remove the stylostome will probably cause a secondary infection that is worse than the original chigger bite. If you do scratch, disinfect the chigger bite with topical antiseptics.

Fortunately, in North America the only real danger from chigger bites is secondary infections that develop after scratching with dirty fingernails. Our chiggers do not carry Lyme disease, Rocky Mountain spotted fever, tularemia or any other disease. Some veterans may recall this is not the case in Asia and the Pacific, where chiggers can transmit disease called scrub typhus. Luckily, Missourians have nothing to fear from chiggers except that terrible itch.

There is no creature alive that can cause more torment for its size than the chigger. By at least knowing what your attacker is and how it operates, you can itch less this summer, and get more enjoyment from your outdoor activities.

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Content revision: 2003.07.24