Demodex

Adults are 0.3–0.4 mm long with semitransparent, elongated bodies consisting of two fused segments. Eight short, segmented legs attach to the anterior segment. The body surface bears scales for anchoring in hair follicles. Pin-like mouthparts are present for feeding on skin cells and sebaceous secretions. D. brevis is slightly shorter than D. folliculorum; females of D. folliculorum are larger and rounder than males.

Hair follicles and sebaceous glands of mammalian skin. In humans, concentrated on the face—particularly near the nose, eyelashes, and eyebrows—with occurrence elsewhere on the body. In canids, D. canis inhabits the dermis. In wolves, lip and chin areas provide the most reliable sampling sites.

Cosmopolitan distribution following mammalian hosts. Human-associated species (D. folliculorum, D. brevis) occur globally, with mite lineages corresponding to host geographic ancestry. Documented in North America, Europe, Africa, and other regions. D. canis occurs on domestic dogs worldwide. D. bovis reported in cattle. Southern European wolves (Iberian and Italian populations) host D. injai, D. canis, D. folliculorum, and D. brevis.

Skin cells (keratinocytes) and sebaceous oils accumulated in hair follicles and glands.

• Homo sapiens - commensal/parasiticHost to D. folliculorum and D. brevis; transmission occurs through close contact with hair, eyebrows, and facial sebaceous glands
• Canis lupus familiaris - commensal/parasiticNatural host of D. canis; puppies typically acquire mites from mothers during nursing
• Canis lupus - commensal/parasiticDocumented host of D. injai, D. canis, D. folliculorum, and D. brevis via qPCR detection in wild populations
• Bos taurus - commensal/parasiticHost to D. bovis; causes subcutaneous nodules in stressed, pregnant, or lactating animals

Eggs are laid inside hair follicles or sebaceous glands. Six-legged larvae hatch after 3–4 days. Larvae develop into adults in approximately 7 days. Total lifespan is several weeks. Mating occurs at the follicle opening with internal fertilization; both sexes possess genital openings.

Mites are nocturnally active, moving slowly on skin surface at 8–16 mm/hour to avoid light. They can leave follicles and walk between adjacent follicles. Transfer between hosts requires close physical contact; mites are not casually transmitted between unrelated individuals. In humans, transmission occurs primarily within families.

Commensal organisms normally controlled by host immune systems. Population regulation by host immunity maintains subclinical infestations. When host immunity is compromised, mite proliferation can cause dermatological disease (demodicosis), altering host skin microenvironment.

Associated with several skin and eye disorders including rosacea, blepharitis, folliculitis, acne vulgaris, seborrheic dermatitis, and psoriasis in immunosuppressed individuals. Demodex blepharitis affects up to 25 million Americans and accounts for over two-thirds of blepharitis cases. Collarettes (cylindrical dandruff at lash bases) are pathognomonic. Treated with topical ivermectin, tea tree oil solutions, and other acaricides. D. canis causes demodectic mange in dogs, particularly in immunocompromised animals.

• Sarcoptes scabieiAlso causes mange in mammals, but burrows in upper skin layers rather than residing in hair follicles; produces different lesion patterns
• Psoroptes bovisCauses psoroptic mange in cattle; feeds by abrading skin surface rather than inhabiting follicles; more prevalent in winter
• Chorioptes bovisCauses chorioptic (foot/leg) mange; primarily affects lower extremities versus follicular distribution of Demodex

• mites
• arachnida
• follicle mites
• commensal
• demodicosis
• blepharitis
• rosacea
• human microbiome
• host specificity
• co-evolution

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Managing External Parasites of Texas Cattle - AgriLife Extension Entomology
• Demodex folliculorum Archives - Entomology Today
• Demodex-folliculorum - Entomology Today
• Humans and Mites Evolved Together, and People from Different Regions Host Different Mite Lineages
• Of Mites and Men: A Visit to the USDA Electron & Confocal Microscopy Unit
• Biology and morphology of Demodex canis
• An Observational, Multicenter, Parallel-Cohort Study Evaluating the Association of Clinical Manifestations and Patient-Reported Outcomes in Patients with Demodex Blepharitis.
• First Detection of Human- and Dog-Associated Demodex Mites (Acari, Arachnida) in Southern European Wolves (Canis lupus).