Cochliomyia hominivorax
(New World screwworm)

Preferred Common Name

• New World screwworm

Other Scientific Names

• Calliphora hominivorax (COQUEREL)
• Callitroga americana (CUSHING & PATTON)
• Callitroga hominivorax
• Cochliomyia americana
• Lucilia hominivorax

International Common Names

• English: flies, screwworm; Primary screwworm; screw worm; screwworm; screwworms in livestock
• Spanish: Gusano Barrenador del Ganado
• French: lucilie bouchere; ver en vis
• Portuguese: bicheira

Local Common Names

• Aruba: Schroefworm
• Germany: Fliege, Schraubenwurm-
• Netherlands Antilles: Schroefworm

EPPO code

• COCLAM (Cochliomyia americana)
• COCLHO (Cochliomyia hominivorax)

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Uniramia
•                 Class: Insecta
•                     Order: Diptera
•                         Family: Calliphoridae
•                             Genus: Cochliomyia
•                                 Species: Cochliomyia hominivorax

The taxonomy and nomenclature of this species was very confused for over 100 years. Cushing and Patton (1933) documented the difference between Cochliomyia americana C & P and Cochliomyia macellaria Fabricius, which served as a key basis in the eradication of Cochliomyia hominivorax from North America, Central America and parts of the Caribbean. Dear (1985) presents an explanation of the taxonomy and nomenclature of C. hominivorax and other members of the Chrysomyini.

Detailed descriptions of the life stages of C. hominivorax are presented in Laake et al. (1936).

Eggs: Eggs are bright white, approximately 1.04 mm long and 0.26 mm in diameter with a cylindrical shape, rounded at the posterior end and flattened at the anterior end with a dorsal seam extending from the anterior end almost to the posterior end of the egg. Eggs are laid in a parallel pattern in layers glued together to form a mass which gives them the appearance of a shingled roof. Eggs are laid in masses which contain from 10 to 400. Eggs are generally laid on or near the edges of wounds but may also be laid on or near host body orifices with purulent discharge. Eggs have also been observed laid approximately 5 cm from the edge of wounds under the moist wool of sheep in Costa Rica during the rainy season (J Welch, personal observation).

Larvae: First instar larvae are approximately 1.2 mm and 0.23 mm, length and diameter, respectively, at hatching and are clear with internal structures visible. Mature first instar larvae are approximately 3.6 mm and 0.57 mm, length and diameter, respectively, and are whitish in colour. Newly molted second instar larvae are generally whitish in colour and are approximately 3.5mm and 0.6mm, length and diameter, respectively. Mature second instar larvae are approximately 6.3 mm to 7.4 mm and 1.5 mm, length and diameter, respectively, and are whitish to cream coloured. Third instar larvae are white to cream to pink coloured depending on diet, and are approximately 6.4 mm to 17 mm in length and 1.6 mm to 3.5 mm in diameter. All larval instars have characteristic bands of spines on most segments and a pair of heavily sclerotized mouth hooks, main tracheal trunks and spiracles. The spiracles with three slit-like openings are almost completely surrounded by heavily sclerotized peritremes, but which appear incomplete ventrally.

Pupae: Pupae are barrel-shaped and dark brown in colour. They are approximately 10.2 mm and 4.3 mm in length and width, respectively.

Adults:Laake (1936) reported that flies are generally deep metallic greenish-blue in colour. Colour is variable, ranging from metallic light to dark green, light grayish-blue through sky-blue to dark blue (J Welch, personal observation). Flies have three dark longitudinal stripes on the dorsal part of the thorax. C. hominivorax adults are approximately 2-3 times the size of a house fly.

Myiasis by C. hominivorax results in a negative economic impact by a decrease in animal weights and milk production, and an increase in animal death. Additionally increase in the costs of inspection and handling of animals, and the increase in costs of insecticides, and veterinary services and medicines results in a negative economic impact (Wyss, 2000). Wyss (2000) reported substantial annual economic benefits to producers (US$ with conversion to 2015 US$ in parentheses) after eradication of C. hominivorax; $896.1 million ($1.25 billion) for the United States of America, $328.6 ($458.5) million for Mexico, and $87.8 ($122.5) million for all of the Central America countries combined. Expanding the analysis of the economic impact of eradicating C. hominivorax from Central America by adding linkages to the economy and consumer benefits resulted in an estimated total annual economic impact of $704.3 ($982.6) million to consumers (Wyss, 2000). Wyss (2002) estimated the annual economic benefits to producers in South America as $2.8 ($3.91) billion.

Impact on habitats is none or unknown.

Impact on biodiversity is low, but may become more important in localized areas during conditions which promote the increase of C. hominivorax populations. Fuller (1962) reported that mortality of fawns of White-tailed deer, Odocoileus virginianus (Zimmerman), ranged from 20 to 80 percent annually depending on environmental and population conditions.

Infestation of humans is under-reported due to the negative social implications. Those humans who cannot take care of themselves are especially vulnerable. Although the young, old, and mentally challenged are more susceptible to myiasis, all humans are potential hosts. Humans living in areas of favorable habitats for C. hominivorax are at a higher risk than those living in unfavorable habitats.

• Invasive in its native range
• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Pioneering in disturbed areas
• Tolerant of shade
• Capable of securing and ingesting a wide range of food
• Highly mobile locally
• Benefits from human association (i.e. it is a human commensal)
• Fast growing
• Has high reproductive potential

• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Host damage
• Increases vulnerability to invasions
• Negatively impacts agriculture
• Negatively impacts cultural/traditional practices
• Negatively impacts human health
• Negatively impacts animal health
• Negatively impacts livelihoods
• Reduced amenity values
• Reduced native biodiversity
• Threat to/ loss of endangered species
• Threat to/ loss of native species
• Damages animal/plant products
• Negatively impacts trade/international relations

• Parasitism (incl. parasitoid)
• Pathogenic
• Rapid growth

• Difficult to identify/detect as a commodity contaminant
• Difficult to identify/detect in the field
• Difficult/costly to control