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Microbiology · Ectoparasites

Dermatobia hominis !

  • Parasite
  • For completeness

Fly larvae living in skin or wounds. The botfly sends its eggs on a mosquito, and its larva forms a boil-like lump with a breathing hole.

Updated 2026-11-01

Also called: human botfly, torsalo, New World screwworm (Cochliomyia hominivorax)

At a glance

Shape
Bottle- or barrel-shaped larva with rows of spines
Family
Oestridae (Dermatobia); Calliphoridae (Cochliomyia)
Type
Insect: fly larva (Diptera)
Size
Mature larva 1–2 cm

Morphology

  • Larva with spines that anchor it in tissue and posterior spiracles for breathing.
  • Identified by its spiracles, mouthparts and cuticular spines.
  • Lesion with a central opening through which the larva breathes.

Transmission

  • Dermatobia: the fly glues its eggs onto a mosquito or other blood-feeding insect (phoresis), which carries them to the skin.
  • Cochliomyia hominivorax: the fly lays eggs directly in wounds or on nasal and oral mucosa.
  • Risk factors: uncovered wounds, chronic ulcers, homelessness or reduced mobility.

Reservoir: Cattle, dogs and other mammals (animal myiasis)

Vector: For Dermatobia, mosquitoes and other blood-feeding insects carry the eggs.

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. The adult Dermatobia fly catches a mosquito or other blood-feeding insect and glues its eggs to it.
  2. When that insect bites a person or animal, the larvae emerge and enter the skin.
  3. The larva lives 5–10 weeks in a cavity under the skin and breathes through a central hole.
  4. When mature, it leaves the skin, drops to the ground and pupates; the adult emerges in a month.
  5. Cochliomyia hominivorax lays its eggs in wounds or mucosa; its larvae eat living tissue.

Virulence factors

  • Dermatobia: painful boil-like nodule with discharge and a feeling of movement.
  • Cochliomyia: extensive destruction of living tissue in wounds, sometimes fatal.
  • Bacterial superinfection of the lesion.
  • Cavity myiasis (nose, orbit, ear) with a risk of serious damage.

Diseases it causes

Clinical picture

  • Inflamed nodule with a central pore that drains fluid and bubbles.
  • Stabbing pain and a feeling that something is moving.
  • Wound or ulcer with visible larvae and a foul smell.

Diagnosis

  • Finding larvae in tissue.
  • Identification of genus or species by morphology (spiracles, mouthparts, spines).
  • Ultrasound or dermoscopy can show the larva.
  • History of travel or rural living.

Treatment

Complete removal of the larvae, often by minor surgery, and daily wound cleaning; antibiotics for superinfection. There is no routine antiparasitic drug.

Drug class only; doses and regimens are set by the clinician from the current guideline.

Prevention

  • Repellents and loose long-sleeved clothing.
  • Cover open wounds and care for chronic ulcers.
  • Mosquito and fly control.
  • In livestock, the sterile male technique against screwworm.

Test yourself

Think of the answer, then tap the question to see it.

How do Dermatobia hominis eggs reach human skin?

Glued to a mosquito or other blood-feeding insect captured by the fly; when it bites, the larvae emerge and penetrate the skin.

Which sign marks a botfly lesion?

A boil-like nodule with a central opening through which the larva breathes.

Which fly causes destructive wound myiasis in the Americas?

Cochliomyia hominivorax, the New World screwworm.

What is the main treatment of myiasis?

Complete removal of the larvae and wound cleaning.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - Myiasis (CDC, 2024); About Myiasis | Myiasis | CDC (CDC, 2024).

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Representative model, for educational purposes only.