Dog follicle mite Demodex canis, copyright Kalumet.

Belongs within: Eleutherengonides.
Contains: Cheyletidae, Myobiidae.

The Cheyletoidea are a group of mites that are commonly parasitic on vertebrates. Representatives include the vermiform Demodicidae which inhabit the hair follicles of mammals, feeding on epithelial and sebaceous gland cells (Walter et al. 2009).

Your little friends that are with you always
Published 9 April 2008
Demodex folliculorum, male above and female below, from Desch and Nutting (1972).

At all times, you are surrounded by life. Micro-organisms swarm on your skin, swim in your gut, and set up shop in your organs. Indeed, at any one time, there are considerably more microbial cells around your person than there even are of your own cells. The micro-organisms are not living on you—you are living among the micro-organisms.

They’re not all bacteria, either. I just thought that I’d briefly introduce you to one of the more distinctive micro-organisms that you are almost certainly carrying about with you—the follicle mite. I also challenge you to keep from scratching yourself while reading this.

Demodex brevis, male on left and female on right, from Desch and Nutting (1972).

.Demodex, the follicle mite, is a specialised inhabitant of the follicles and pores of mammalian skin. A significant number of species appear to have been described from different hosts, ranging from humans to dogs to cattle to marsupial mice to honest-to-goodness mice. The most distinctive feature of Demodex is its elongate body shape, which allows it to live head-first inside the follicles of its host, feeding on cells within the follicle. Humans are actually inhabited by two species, Demodex folliculorum and D. brevis (Desch & Nutting 1972). The more elongate D. folliculorum lives in the follicles themselves, and feeds on the epithelial lining. The rarer D. brevis is shorter, and is found within the sebaceous gland on which it feeds. Demodex brevis is found on less people, and also at lower numbers—multiple D. folliculorum may be found in a single follicle (as shown below in an image from here), but usually only one D. brevis.

The question of whether Demodex causes any harm to its human host is a difficult one. The sheer universality of Demodex within the human population implies that its presence is usually of no concern to the host. However, another species, D. canis, is widely connected with mange in dogs, and Demodex has been connected with skin disorders (demodicidosis) in a number of humans. The difficult question is whether Demodex is a direct causative agent or not. As one might reasonably expect Demodex to be present anyway, it’s mere presence at an infection site does not automatically indicate its responsibility for the infection. It seems likely that Demodex may be a facultative agitator of problems arising from other ultimate causes, such as a suppressed immune system (Jansen et al. 2001) or an already-damaged follicle (Pena & Andrade Filho 2000). It is noteworthy in this light that prevalence of demodicidosis varies seasonally (it is most common in spring), but the prevalence of Demodex itself does not (Desch & Nutting 1972). Demodex folliculorum may cause damage when more than six individuals are present in the same follicle (Desch & Nutting 1972).

Systematics of Cheyletoidea

Characters (from Walter et al. 2009): Soft bodied but often with weak dorsal shields. Gnathosoma well defined, composed of cheliceral stylophore either free from subcapitulum or fused into gnathosomatic capsule; movable cheliceral digits styliform, needle-like, retractile, approximate terminally; palpi variously developed, often reduced with fused tibiotarsus and femorogenu, or telescoped, sometimes large and armed with a distinctive tibial claw; postcheliceral stigmata and peritremes present in free-living and some parasitic forms but absent in many parasites; with present, peritremes at base of chelicerae or on dorsal surface of gnathosomatic capsule, dorsal cheliceral seta rd absent in larva. Prodorsum lacking anteromedian naso, typically with four pairs of setae, none inserted in bothridia; eyes present or absent. Opisthosoma with 0 to many setae dorsally and laterally, with or without postlarval setal additions or hypertrichy dorsally; cupules (lyrifissures) absent; elements of opisthosomatic segments AD absent. Larval urstigma and postlarval genital papilla absent. Claws always present on tarsi II, and usually on tarsi III-IV unless legs are reduced or absent, claws present or absent on tarsus I; empodia present or absent, often with tenent hairs; genua and tibiae of all legs with a maximum of three setae; solenidion of genu I present or absent. Female genital opening ventral, terminal or dorsal, free from or fused to anal opening; oviporus adjacent to or fused with genital opening. Male with terminal or dorsal genito-anal opening. Usually four active postembryonic instars including larva, two nymphal instars, and adult. Developmental stases may be apodous, or postlarval stases may be hexapod.

<==Cheyletoidea [Demodicoidea, Lipostigmata]
    |  `--SyringophilidaeBF01
    |       |  i. s.: Syringophiloides minorWP99
    |       |         Syringophilopsis Kethley 1970H98
    |       |         AulonastusK09
    |       |         CrotophagisyringophilusDPD16
    |       |         Torotrogia merulaeDPD16
    |       |--Syringophilus Heller 1880H98 [SyringophilinaeWL09]
    |       |    |--S. bipectinatus Heller 1880SMD01
    |       |    `--S. columbaeL55
    |       `--PicobiinaeWL09
    |            |--Calamincola lobatus (Castro 1977)WL09, SMD01
    |            `--PicobiaSMD01
    |                 |--P. dryobates (Fritsch 1958) [=Syringophilus dryobates]SMD01
    |                 |--P. dziabaszewskiiDPD16
    |                 |--P. khulkhshani (Kivganov & Sharafat 1995)SMD01
    |                 `--P. polonica Skoracki, Magowski & Dabert 2001SMD01
       `--Demodicidae [Demodecidae, Demodides]DPD16
            |--Rhinodex Fain 1959B91
            |--Pterodex Lukoschus, Woeltjes et al. 1980B91
            |--Soricidex Bukva 1982B91
            |--Stomatodex Fain 1959B91
            |    `--S. cercarteti Desch 1991 [=Demodex cercateti]H98
            |--Ophthalmodex Lukoschus & Nutting 1980B91
            |    |--O. australiensis Woeltjes & Lukoschus 1981 [=Opthalmodex (l. c.) australiensis]H98
            |    |--O. molossiWL09
            |    `--O. wilsoni Woeltjes & Lukoschus 1981H98
            `--Demodex Owen 1843B91
                 |--D. acutipesB91
                 |--D. antechini Nutting & Sweatman 1970H98
                 |--D. auratiN91
                 |--D. bicaudatus Kniest & Lukoschus 1981H98
                 |--D. bovis Stiles 1892B91 [=D. folliculorum var. bovisH98]
                 |--D. brevis Akbulatova 1963B91 [=D. folliculorum var. brevisH98]
                 |--D. canis Leydig 1859H98
                 |--D. caprae Railliet 1893 [=D. folliculorum var. caprae]H98
                 |--D. cati Mégnin 1877 [=D. folliculorum var. cati]H98
                 |--D. cricetiN91
                 |--D. equi Railliet 1893 [=D. folliculorum var. equi]H98
                 |--D. flagellurus Bukva 1985B91
                 |--D. folliculorum (Simon 1842)B91 [=Acarus folliculorumH98]
                 |--D. kutzeri Bukva 1987B91
                 |--D. longissimusWL09
                 |--D. macroglossi Desch 1981H98
                 |--D. melesinusH23
                 |--D. nanus Hirst 1918B91
                 |--D. odocoileiN91
                 |--D. ovis Hirst 1919B91 [=D. canis var. ovisH98]
                 |--D. phylloides Csokor 1879H98
                 |--D. rosus Bukva 1985B91
                 |--D. sabani Desch, Lukoschus & Nadchatram 1984B91
                 |--D. sciurinus Hirst 1923H23
                 |--D. tauri Bukva 1986B91
                 `--D. zalophi Dailey & Nutting 1980H98
Cheyletoidea incertae sedis:
    |--Psorergatoides Fain 1959H98
    |    `--P. australiensis Giesen et al. 1982H98
    |    |--P. glaucomysWL09
    |    `--P. talpaeWL09
    `--Psorobia Fain 1959H98
         |--P. bosWL09
         |--P. foinaeWL09
         |--P. mustelaeWL09
         `--P. ovis (Womersley 1941) [=Psorergates ovis]H98
  Harpirhynchidae [Ophioptidae]BF01
    |--Harpyrhynchus Mégnin 1877WL09, H98 [HarpirhynchinaeWL09, Harpyrhynchinae]
    |    |--H. kakatoe Fain 1972 [=Harpirhynchus kakatoe]H98
    |    |--H. monstrosus Fritsch 1954 [=Harpirhynchus monstrosus]H98
    |    |--H. novoplumarisWL09
    |    `--H. rosellacinus Lawrence 1959 [=Harpirhynchus rosellacinus]H98
    `--Ophioptes Sambon 1928H98 [OphioptinaeWL09]
         |--O. parkeriWL09
         |--O. samboni Southcott 1956H98
         |--O. southcottiWL09
         `--O. tropicalisWL09

*Type species of generic name indicated


[BF01] Bochkov, A. V., & A. Fain. 2001. Phylogeny and system of the Cheyletidae (Acari: Prostigmata) with special reference to their host-parasite associations. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique Entomologie 71: 5–36.

[B91] Bukva, V. 1991. Structural reduction and topological retrieval: problems in taxonomy of Demodicidae. In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 1 pp. 293–300. SPB Academic Publishing: The Hague.

[DPD16] Dabert, M., H. Proctor & J. Dabert. 2016. Higher-level molecular phylogeny of the water mites (Acariformes: Prostigmata: Parasitengonina: Hydrachnidiae). Molecular Phylogenetics and Evolution 101: 75–90.

Desch, C., & W. B. Nutting. 1972. Demodex folliculorum (Simon) and D. brevis Akbulatova of man: redescription and reevaluation. Journal of Parasitology 58 (1): 169–177.

[H98] Halliday, R. B. 1998. Mites of Australia: A checklist and bibliography. CSIRO Publishing: Collingwood.

[H23] Hirst, S. 1923. On some new or little-known species of Acari. Proceedings of the Zoological Society of London 1923: 971–1000.

Jansen, T., U. Kastner, A. Kreuter & P. Altmeyer. 2001. Rosacea-like demodicidosis associated with acquired immunodeficiency syndrome. British Journal of Dermatology 144 (1): 139–142.

[K09] Krantz, G. W. 2009. Habits and habitats. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 64–82. Texas Tech University Press.

[L55] Lavoipierre, M. M. J. 1955. On two new species and new records of Acarina mainly from the Ethiopian region. Parasitology 45 (1–2): 121–127.

[N91] Nutting, W. B. 1991. Demodecosis, treatment and prevention. In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 1 pp. 309–317. SPB Academic Publishing: The Hague.

Pena, G. P., & J. de S. Andrade Filho. 2000. Is Demodex really non-pathogenic? Revista do Instituto de Medicina Tropical de São Paulo 42 (3): 171–173.

[SMD01] Skoracki, M., W. Magowski & J. Dabert. 2001. Picobia polonica sp. n. (Acari: Prostigmata: Syringophilidae), a new species of quill mite from the domestic hen, Gallus gallus domesticus (Aves: Phasianidae). Folia Parasitologica 48: 154–158.

[WL09] Walter, D. E., E. E. Lindquist, I. M. Smith, D. R. Cook & G. W. Krantz. 2009. Order Trombidiformes. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 233–420. Texas Tech University Press.

[WP99] Walter, D. E., & H. C. Proctor. 1999. Mites: Ecology, Evolution and Behaviour. CABI Publishing: Wallingford (UK).

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