Ohio State University Extension Fact Sheet

Entomology

1991 Kenny Road, Columbus, Ohio 43210-1000

Chiggers

HYG-2100-98

Common Name	Scientific Name
Chigger	Trombicula alfreddugesi (Oudemans)
Jigger
Red Bug

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.

Identification

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.

Life Cycle and Habits

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.

Bites

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.

Control Measures

Skin Care

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.)

Prevention

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.

Insecticides

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.