|Common Name||Scientific Name|
|Chigger||Trombicula alfreddugesi (Oudemans)|
Probably no creature on earth can cause as much torment for its size than the tiny chigger. Tiny six-legged chigger larvae attack campers, picnickers, hikers, bird watchers, berry pickers, fishermen, soldiers, and homeowners in low, damp areas where vegetation is rank such as woodlands, berry patches, orchards, along lakes and streams, and even in drier places where vegetation is low such as lawns, golf courses, and parks. They are most numerous in early summer when grass, weeds and other vegetation are heaviest. Chiggers do not burrow into the skin, but insert their mouthparts in a skin pore or hair follicle. Their bites produce small, reddish welts on the skin accompanied by intense itching as irritating as acute cases of poison ivory or poison sumac. These symptoms often are the only way of learning that an outdoor area is infested since chiggers are so small that most cannot be seen without a magnifying glass. Chiggers feed on a wide variety of snakes, turtles, birds, and small mammals as well as humans.
Chigger mites are about 1/20 inch long, usually bright red, have hairy bodies, and travel rapidly. The larval stage has three pairs of legs whereas the nymph and adult stage have four pairs of legs. There is a marked constriction in the front part of the body in the nymph and adult stage. Larvae are orange, yellow or light red and about 1/150 to 1/120 inch in diameter. Eggs are globular-shaped.
Adult chiggers overwinter near or slightly below the soil and in other protected places. Females become active in the spring and lay up to 15 eggs per day in vegetation when soil temperatures are 60°F. Eggs hatch into six-legged larvae, the only stage that attacks humans and animals (parasitic stage). After hatching, chigger larvae climb up onto vegetation from which they can more readily snag a passing host. After engorgement, often requiring one to several days, larvae drop off the host and transform into eight-legged nymphs which mature to the adult stage. Nymphs and adults feed on eggs of springtails, isopods, and mosquitoes. The life cycle is about 50 to 70 days, with adult females living up to one year and producing offspring during this time. Multiple generations occur in warmer climates, whereas only two to three develop each season in some northern states. Chiggers are usually encountered in late spring and summer in areas where weeds and briars have overgrown. They lurk on grass stems, leaves, shrubbery, etc., usually in damp, shaded spots near the top of different objects close to the soil. Young chiggers attach themselves to the skin of people, domestic animals, wild animals (including reptiles), poultry and birds. The preferred feeding locations on people are parts of the body where clothing fits tightly over the skin such as around the belt line, waistline, under girdles and under socks, or where the flesh is thin, tender or wrinkled such as the ankles, in the armpits, back of the knees, in front of the elbow, or in the groin.
Chigger larvae do not burrow into the skin, nor suck blood. They pierce the skin and inject into the host a salivary secretion containing powerful, digestive enzymes that break down skin cells that are ingested (tissues become liquefied and sucked up). Also, this digestive fluid causes surrounding tissues to harden, forming a straw-like feeding tube of hardened flesh (stylostome) from which further, partially-digested skin cells may be sucked out. After a larva is fully fed in four days, it drops from the host, leaving a red welt with a white, hard central area on the skin that itches severely and may later develop into dermatitis. Any welts, swelling, itching, or fever will usually develop three to six hours after exposure and may continue a week or longer. If nothing is done to relieve itching, symptoms may continue a week or more. Scratching a bite may break the skin, resulting in secondary infections. However, chiggers are not known to transmit any disease in this country.
After returning from a chigger-infested area, launder the field clothes in soapy, hot water (125°F.) for about half an hour. Infested clothes should not be worn again until they are properly laundered and/or exposed to hot sunshine. Unlaundered clothes or those laundered in cool water will contain the biting chiggers to again reinfest your skin. As soon as possible, take a good hot bath or shower and soap repeatedly. The chiggers may be dislodged, but you will still have the stylostomes, causing the severe itch. Scratching deep to remove stylostomes can cause secondary infections. For temporary relief of itching, apply ointments of benzocaine, hydrocortisone, calamine lotion, New Skin, After Bite, or others recommended by your pharmacist or medical doctor. Some use Vaseline, cold cream, baby oil, or fingernail polish. (The sooner the treatment, the better the results.)
Mowing of briars, weeds, and thick vegetation and close clipping of lawns, to eliminate shade and moisture, will reduce chigger populations, and permit sunlight and air to circulate freely. Chigger larvae can penetrate many types of clothing, but high boots and trousers of tightly woven fabric tucked into stockings or boots help deter them.
Before going into an area where chiggers may be present, protect yourself by using a repellent such as deet (Off MGK, Muskol, Detamide, Metadelphene, Repel, Diethy-toluamide) or permethrin available at many drugstores or hardware stores. Deet-based repellents are effective for only a few hours, whereas permethrin-based repellents are for use only on clothing and effective for several days. Apply the repellent to both the skin and clothing, especially on hands, arms, or legs, if uncovered, and to clothing openings at cuffs, neck, waistband, and upper edges of socks. Follow label directions since repellents may damage plastics, nail polish, and painted or varnished surfaces. Do not use indiscriminately as severe human allergies can develop. Keep moving since the worst chigger infestations occur when sitting or laying down in a sunny spot at midday with temperatures above 60°F. If possible, stick to roads and trails.
Treating known chigger trouble spots is quicker and less expensive than treating an entire area. Place six-inch squares of black cardboard on edge in the grass and observe for a few minutes. Any small, yellowish or pinkish chiggers present will climb rapidly to the top of the square and congregate there. Make tests in 10 to 12 different spots such as grass, dead leaves, briars, weeds, etc. Unless the entire area is infested, treat only the spots where control is desired such as grass around picnic tables, lawn chairs, or recreational equipment. Chiggers tend to concentrate in "mite islands" while nearby spots are free of them. They become rather inactive at temperatures below 60°F.
Outdoor sprays of chlorpyrifos (Dursban), carbaryl (Sevin) or diazinon will give control. Only the licensed pest control operator or applicator can use certain formulations of propoxur (Baygon), cyfluthrin (Tempo), or fluvalinate (Marvik, Yardex). Treat the grass, shrubs, and trees in lawns, parks, campgrounds and golf courses, if needed, keeping humans and pets off treated areas until dry. Retreatment may be needed after two to three weeks in heavy chigger infestations. Before using any pesticide, always read the label and follow directions and safety precautions.
Do not wear dog or cat flea collars on your ankles or cattle ear tags on your shoes to ward off chiggers. It is very dangerous resulting in chemical skin burns and toxic effect to the wearers.
NOTE: Disclaimer - This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registrations, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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