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Demodex folliculorum

By Aisha Rush

Geographic Range

These mites are distributed worldwide as commensals of humans. It is unknown from what region they originated, they have been associated with humans throughout their evolutionary history. They inhabit the hair follicles of most if not all humans. They infest areas around the nose, in the ear canals, and around the eyelids. (Woolley 1988)

Habitat

The habitat for this mite is inside the hair follicle of a human. (Baker 1952, Woolley 1988)

Physical Description

These are weakly colored mites--probably to enable them to blend in with their environment (the human skin). They are also very small, ranging in length from .10 to .39mm. They are cigar shaped with eight short and stubby legs. Like most mites, they exhibit no segmentation and have a completely fused cephalothorax and abdomen. They also have simple eyes. The mouth or head region contains chelicerae (which helps to classify them in the subphylum chelicerata) that are greatly reduced, reducing the gnathosoma to a stubby structure. This particular mite does show sexual dimorphism in that the female mite appears to be shorter than the male with a more rounded body. The male tends to be a little longer than the female and much more slender in appearance. (Baker 1952, Woolley 1988)

Reproduction

The entire life of the mite is spent on the host. They cannot be obtained from any other animal besides humans. Reproduction occurs through internal fertilization. The abdomen of both male and female mites bear genital openings. Their life cycle is usually complete in 18-24 days. The adult female mite lays 20-24 eggs in a hair follicle. These eggs are nourished and incubated by the cells surrounding them within the follicle. After the eggs hatch and the nymphs emerge, they are similar to the adults but only have six legs rather than eight. The remaining two legs grow during as the nymph develops into an adult (anamorphism). (Baker 1952)

  • Breeding season
    Reproduction occurs throughout the year.
  • Average number of offspring
    20-24

Behavior

Much of their behavior is expressed through their eating and reproductive habits.

Food Habits

Demodex folliculorum are housed in hair follicles; they derive their nourishment from the cells of the host. Their main source of food is human glandular secretions within these follicles. It is also here where the larvae are nourished and grow into the adult form of the mite. (Baker 1952)

  • Animal Foods
  • body fluids

Economic Importance for Humans: Positive

There is no specific harm to humans from these mites. Hair follicle mites share a commensalistic relationship with humans in that they benefit from their association with humans, but the host is unharmed.

Economic Importance for Humans: Negative

Some people may have allergic reactions to these mites. Such reactions may cause hair loss or the development of acne.

Conservation Status

Hair follicle mites are common worldwide.

Contributors

Aisha Rush (author), University of Michigan-Ann Arbor, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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carnivore

an animal that mainly eats meat

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

fertilization

union of egg and spermatozoan

internal fertilization

fertilization takes place within the female's body

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

year-round breeding

breeding takes place throughout the year

References

1994. "Mites: Ecological and Evolutionary Analyses of Life-History Patterns.". New York: London:Chapman and Hall.

Baker, E. 1952. An Introduction to Acarology. New York: The MacMillan Company.

Prasad, V. 1988. Mites: A Bibliography. Michigan: Indira Publishing House.

Vercammen-Grand Jean, P. 1968. The Chigger Mites of the Far East. Washington: U.S. Army Medical and Development Command.

Woolley, T. 1988. Acarology: Mites and Human Welfare. New York: Wiley Interscience.

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