Chiggers
(Chigger Bites)
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
What are chiggers?
Chiggers are the juvenile form (larvae) of a certain type of mite of the
family Trombiculidae. Mites are arachnids (like spiders and ticks).
Chiggers are found throughout the world. They most commonly live in forests,
grassy fields, gardens, parks, and in moist areas around lakes or rivers. Most
of the larvae that cause chigger bites are found on plants that are relatively
close to the ground surface, because they require a high level of humidity for
survival.
What do chiggers look like?
Chiggers are barely visible to the naked eye (their length is less than
1/150th of an inch). They are red in color and may be best appreciated when
clustered in groups on the skin. The juvenile forms have six legs, although the
(harmless) adult mites have eight legs.
Picture of Chigger Eggs, Larvae, Nymph, and Adult
How do chiggers bite humans?
Chigger mites infest human skin via areas of contact with vegetation, such as
pant cuffs or shirt sleeves and collars. They migrate on the skin in search of
an optimal feeding area. A common myth about chiggers is that they burrow into
and remain inside the skin. This is not true. Chiggers insert their feeding
structures into the skin and inject enzymes that cause destruction of host
tissue. Hardening of the surrounding skin results in the formation of a feeding
tube called a stylostome. Chigger larvae then feed upon the destroyed tissue. If
they are not disturbed (which is rarely the case because of they cause
substantial itching) they may feed through the stylostome for a few days.
The chigger's mouth and feeding structures are delicate and are best able to
penetrate the skin at areas of wrinkles, folds, or other
areas of skin that are thin. Most bites
occur around the ankles, the crotch and groin areas, behind the
knees, and in the armpits. Barriers to migration on the skin such as belts may
be one reason that chigger bites also commonly occur at the waist or at other
areas where their migration is prevented by compression from clothing.
Next: What are the symptoms of chigger bites? »
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