Kurzgesagt – In a Nutshell 

Sources – Mutant Flies

- Cochliomyia hominivorax – which literally means "the man eater." The New World Screwworm fly, at home in the Americas.. Each of these metallic blue-green flies with bright red eyes that exist in nature is here because it feasted on the flesh of a warm blooded animal. Cochliomyia can detect wounds and smell blood across vast distances. If a human, a deer or a squirrel has the tiniest scratch, female screwworm flies will try to lay eggs in the wound. When they hatch the worms start eating healthy flesh with sharp mandibles. Causing horrible wounds, attracting even more flies. In serious cases the animal will die, at least be severely weakened. 

#WOAH (retrieved 2025): New world screwworm (Cochliomyia hominivorax)

https://www.woah.org/en/disease/new-world-screwworm-cochliomyia-hominivorax/ 

Quote: “The New World screwworm (NWS), Cochliomyia hominivorax (Coquerel), is an obligate parasite of mammals, including humans, during their larval stages. It belongs in the subfamily Chrysomyinae of the family Calliphoridae of the order Diptera (true flies). Larvae feeding on the skin and underlying tissues of the host cause a condition known as wound or traumatic myiasis, which can be fatal. Infestations are generally acquired at sites of previous wounding, due to natural causes or to animal husbandry practices, but they may also occur in the mucous membranes of body orifices. Female flies are attracted to wounds, at the edges of which each female lays an average of 343 eggs. The larvae emerge within 12–24 hours and immediately begin to feed, burrowing head-downwards into the wound. After developing through three larval stages (instars) involving two molts, the larvae leave the wound and drop to the ground, into which they burrow to pupate. The duration of the life-cycle off the host is temperature dependent, being shorter at higher temperatures, and the whole cycle may be completed in less than 3 weeks in the tropics. Treatment is generally effected by application of organophosphorus insecticides into infested wounds, both to kill larvae and to provide a residual protection against reinfestation. Preventive measures include the spraying or dipping of susceptible livestock with organophosphorus compounds and, more recently, use of avermectins (especially doramectin) as subcutaneous injections to animals ‘at risk’. Strict control of the movement of animals out of affected areas also acts as a preventive measure. There are no vaccines or biological products available, except for the use of sterilised male flies in the sterile insect technique (SIT). In this technique, vast numbers of sterilised male flies are sequentially released into the environment, where their matings with wild females produce infertile eggs, leading to an initial population reduction and, progressively, eradication. The zoonotic implications are considerable because humans, especially the young, elderly or infirm, can be infested, with severe and sometimes fatal consequences.”

USDA (2025): New World Screwworm. What you need to know.

https://www.aphis.usda.gov/sites/default/files/bro-new-world-screwworm.pdf 

Quote: “Screwworm infestations begin when a female fly lays eggs on a wound or orifice of a live warm-blooded animal. Female flies are attracted to the odor of a wound or opening such as the nasal or eye openings, umbilicus of a newborn, or genitalia. Wounds as small as a tick bite may attract a female to feed. One female can lay up to 3,000 eggs in her lifespan. Eggs hatch into larvae that burrow into the wound to feed on the living flesh. After about 7 days of feeding, larvae drop to the ground, burrow into the soil, and pupate. The adult screwworm fly emerges from the soil after 7–54 days depending on temperature and humidity. Female flies mate after 3 days, and males can mate within 24 hours of maturation.”

CDC (2024): Clinical Overview of New World Screwworm Myiasis. 

https://www.cdc.gov/myiasis/hcp/clinical-overview/index.html 

Quote: “New World screwworm (NWS) infestation is a type of myiasis that occurs when NWS fly larvae (Cochliomyia hominivorax) infest the living flesh of warm-blooded animals—most commonly livestock and less commonly birds, pets, and humans. The screwworm flies are attracted to and lay their eggs on and in open wounds and mucous membranes.

The name screwworm refers to the feeding behavior of the larvae (maggots) as they burrow (screw) into healthy tissue. NWS larvae cause extensive damage by tearing into the host's tissue with sharp mouth hooks. The wound can become larger and deeper as more larvae hatch and feed on living tissue. As a result, NWS can cause serious damage to the animal or person it infects. Bacterial superinfection can also occur because of the NWS infestation.

(...)

New World screwworm infestations begin when a female fly lays eggs on a wound or orifice of a live, warm-blooded animal. The odor of a wound or an opening such as the nasal or eye openings, umbilicus of a newborn, or genitalia attracts female flies. Wounds as small as a tick bite may attract a female fly to feed. One female can lay 200 – 300 eggs at a time and may lay up to 3,000 eggs during her 10- to 30-day lifespan.

Eggs hatch into larvae that burrow into the wound to feed on the living flesh. After about 7 days of feeding, larvae drop to the ground, burrow into the soil, and pupate. The adult screwworm fly emerges from the soil after 7 – 54 days depending on temperature and humidity. Female flies mate only once in their lifespan.”

WOAH (2019): Chapter 3 .1.1 5 . New World Screwworm (Cochliomyia hominivorax) and Old World Screwworm (Chrysomya bezziana). 

https://www.woah.org/fileadmin/Home/eng/Health_standards/tahm/3.01.15_SCREWW.pdf 

Quote: “Screwworm larvae pass through three stages (or instars), separated by cuticular molts that facilitate rapid growth, and they reach maturity about 5–7 days after egg hatch. They then stop feeding and leave the wound, falling to the ground into which they burrow and pupate. The pupa develops within the puparium, a barrel-shaped protective structure formed by hardening and darkening of the cuticle of the mature larva. On completion of development, adult flies usually emerge from the puparium in the morning and work their way up to the soil surface, where they extend their wings for hardening prior to flight. Males become sexually mature and able to mate within 24 hours, but the ovaries of females need to mature over 6–7 days, and females only become responsive towards males, mating when about 3 days old. About 4 days after mating, female flies are ready to oviposit. They seek a suitable host and lay their eggs, all oriented in the same direction, like a tiled roof, firmly attached to each other and to the oviposition substrate. The numbers of eggs laid per batch vary depending on many factors (e.g. fly strain, disturbance during oviposition), but the average first batch has in the order of 175 eggs for OWS and 343 for NWS (Spradbery, 1994). Following the first egg batch, further batches are laid at intervals of 3–4 days (Thomas & Mangan, 1989). Adult flies live on average for 2–3 weeks in the field during which time they feed at flowers, and the females also take in protein, e.g. from serous fluids at animal wounds and decomposing animals. The rate of development of the immature stages is influenced by environmental and wound temperatures, being slower at low temperatures, although true diapause does not occur. This effect is most pronounced in the off-host pupal stage, which can vary from 1 week to 2 months’ duration depending on the season (Laake et al., 1936). Thus, the complete life cycle of NWS may take 2–3 months in cold weather, whereas in temperate conditions with an average air temperature of 22°C, it is completed in about 24 days (James,1947), and in tropical conditions averaging 29°C it is completed in about 18 days (Thomas & Mangan, 1989).” 

#COPEG (2022): Life Cycle of the Fly

https://copeg.org/en/about-the-screwworm/

- For most of history, this parasite was simply a horrifying fact of life in the Americas. And then we accidently created a paradise for them. As farmers introduced millions and millions of cows to the vast expanses of the southern US, screwworms became a catastrophic problem and a source of endless suffering for our defenseless cattle.

#Richardson, R. H. et al. (1982): Autocidal Control of Screwworms in North America. Science, Vol. 215

https://www.science.org/doi/10.1126/science.7199204 

Quote: “Periodic outbreaks of screwworms did not become a serious problem in livestock (5) in the United States until the late 1800's, when there was a large increase in the number of cattle in the Southwest. New cattle trails ard the construction of railroads and windmills (6) after the Civil War made markets and water more accessible and allowed Texas to become blanketed with cattle (7, 8). The windmills were used to fill waterholes so that even in periods of drought water was usually available (9). A similar year-round water supply was achieved in areas of adequate seasonal rainfall by constructing earthen ponds. The great increase in cattle led to increasing outbreaks of screwworms which, by the turn of the century, were becoming an annual curse on ranches in central Texas and along the Gulf Coast (10). 

(...)

Ecological changes caused by the increase in cattle also occurred on either side of the U.S.-Mexico border from Texas to California. -In addition to the overgrazing, barbed wire fences became common after World War I. Sheep had usually been kept in flocks on open ranges tended by shepherds, but when the ranges were fenced the sheep were not as closely observed (16). Thus screwworm-infested wounds were less likely to be treated and the larvae could complete their life cycles.”

- Traditional pesticides were useless against Cochliomyia because you couldn't poison something that lived inside a living animal's flesh. You couldn't prevent animals from getting injured or flies from finding wounds. The situation seemed hopeless and the Cochliomyia was winning. Ranchers had to spend countless hours examining their herds, treating wounds, trying to protect newborns, watching helplessly as their animals suffered.

Even if there were products to treat the affected animals, there was no product that could simply be used to spray entire herds as a prophylactic measure. 

#USDA (retrieved 2025): The New World Screwworm

https://www.nal.usda.gov/exhibits/speccoll/exhibits/show/stop-screwworms--selections-fr/introduction 

Quote: “Treating infested livestock was a highly unpleasant, labor-intensive job. Ranchers had to check livestock often for infested wounds, and infested animals had to be treated and confined. Wound treatments progressed from pine tar oil to various smears of insecticide notable for their highly unpleasant odor. In 1935, screwworms resulted in 180,000 livestock deaths in under half the counties in Texas, in spite of the manpower and constant effort invested in keeping the insects at bay. Endemic to the Southwest, screwworms spread to the Southeast when producers unknowingly transported infested livestock there in 1933.”

#Klassen, W. & Curtis C.F. (2005): History of the Sterile Insect Technique

https://link.springer.com/chapter/10.1007/1-4020-4051-2_1 

Quote: “Since ancient times, the tropical and semi-tropical New World screwworm has been a serious enemy of warm-blooded animals, including humans, in an area extending from Argentina to the southern USA. Descendants of European settlers managed their herds and flocks so that the birth of most calves and lambs, as well as castration, branding, and dehorning operations, occurred only during months when screwworms were scarce. Each animal was checked for wounds at least twice per week, and each wound was treated with an insecticidal “smear” (Knipling 1985). “

#USDA (retrieved 2025): The New World Screwworm

https://www.nal.usda.gov/exhibits/speccoll/exhibits/show/stop-screwworms--selections-fr/introduction 

Quote: “USDA estimates that the U.S. livestock industry benefits by more than $900 million a year as a result of the eradication of the screwworm. Mexican producers and consumers saved about $2 billion from the beginning of eradication to 1991. A 1995 Texas A&M University study evaluated the direct benefit to the Central America livestock producers at $73 million a year and overall economic benefits to the region at $257 million annually. The benefits to Mexico were estimated at $275 million annually from 1991 to 1994. In addition there are the benefits of enhanced human and animal health and increased standards of living due to the removal of this deadly insect. Endangered wild species have a better chance of survival. Additional grazing areas previously subject to high rates of screwworm infestation are now available for use by livestock and wildlife. The quality of life for smaller farmers and ranchers, especially in Central America, was improved by relief from lost man-hours needed to treat livestock and risk of loss from screwworm infestation. These benefits were made possible by the close cooperation of federal and state governments, individual producers, and producers' alliances to financially support eradication, as well as with activities that tracked infestations and allowed them to be treated. USDA scientists, primarily from the Agricultural Research Service (ARS) and Animal and Plant Health Inspection Service (APHIS), achieved the scientific and technical advances that made eradication possible.

(...)

Treating infested livestock was a highly unpleasant, labor-intensive job. Ranchers had to check livestock often for infested wounds, and infested animals had to be treated and confined. Wound treatments progressed from pine tar oil to various smears of insecticide notable for their highly unpleasant odor. In 1935, screwworms resulted in 180,000 livestock deaths in under half the counties in Texas, in spite of the manpower and constant effort invested in keeping the insects at bay. Endemic to the Southwest, screwworms spread to the Southeast when producers unknowingly transported infested livestock there in 1933.”

- And then two scientists in the 1950s had an idea that was too wild to be taken seriously at first. What if we make screwworms radioactive? 

#Klassen, W. & Curtis C.F. (2005): History of the Sterile Insect Technique

https://link.springer.com/chapter/10.1007/1-4020-4051-2_1 

Quote: “During the 1930s and 1940s the idea of releasing insects of pest species to introduce sterility (sterile insect technique or SIT) into wild populations, and thus control them, was independently conceived in three extremely diverse intellectual environments. The key researchers were A. S. Serebrovskii at Moscow State University, F. L. Vanderplank at a tsetse field research station in rural Tanganyika (now Tanzania), and E. F. Knipling of the United States Department of Agriculture. Serebrovskii’s work on chromosomal translocations for pest population suppression could not succeed in the catastrophic conditions in the USSR during World War II, after which he died. Vanderplank used hybrid sterility to suppress a tsetse population in a large field experiment, but lacked the resources to develop this method further. Knipling and his team exploited H. J. Muller’s discovery that ionizing radiation can induce dominant lethal mutations, and after World War II this approach was applied on an area-wide basis to eradicate the New World screwworm Cochliomyia hominivorax (Coquerel) in the USA, Mexico, and Central America. 

(...)

Runner (1916) found that large doses of X-rays applied to the cigarette beetle Lasioderma serricorne (F.) rendered it incapable of reproduction. Soon afterwards H. J. Muller (1927) showed that ionizing radiation induced visible mutations in Drosophila, and also a much larger number of dominant lethal mutations, which were expressed through a reduction in the hatch of eggs laid by treated females or fathered by treated males. However, only after 1950, when Muller made a special effort to publicize the biological effects of radiation, did economic entomologists become aware that, through irradiation, sexual sterility in male insects was quite easily achieved (Bakri et al., this volume). 

Nevertheless, already in the 1930s and 1940s, the idea of releasing pest insects to introduce sterility into wild populations, and thus control them, had been conceived independently by A. S. Serebrovskii at Moscow State University, F. L. Vanderplank at a tsetse field research station in rural Tanganyika (now Tanzania), and E. F. Knipling of the United States Department of Agriculture (USDA). 

Serebrovskii and Vanderplank both sought to achieve pest control through the sterility that arises when different species or genetic strains are hybridized (Robinson, this volume). The debut of the most successful AW-IPM programme integrating the SIT to date occurred in the 1950s. It was started to rid the south-eastern USA of the New World screwworm Cochliomyia hominivorax (Coquerel), a deadly parasite of livestock. 

(...)

In 1946, H. J. Muller was awarded the Nobel Prize in Medicine for his discovery of induced mutagenesis, and this gave him the prestige to lead a vigorous campaign against the atmospheric testing of atomic weapons. He wrote a popular article in the American Scientist in which he used tombstones as symbols to depict graphically the dead progeny from matings of irradiated Drosophila (Muller 1950). A. W. Lindquist recognized that Muller had developed a means of sexually sterilizing insects, and drew Knipling’s attention to this paper. Knipling wrote to Muller, asking if ionizing radiation could be used to induce sexual sterility in the New World screwworm. Upon receiving Muller’s confident assurance, Bushland and D. E. Hopkins used the X-Ray Therapy Section of Brooke Army Hospital to conduct the first screwworm irradiations. They found that, when 6-day-old pupae were exposed to 50 Gy, the adults that emerged appeared to be normal. However, when irradiated males were mated with untreated females, none of the eggs hatched. Females that had been irradiated and mated to untreated males produced almost no eggs, and none hatched. When untreated and irradiated males were caged together with untreated females, the irradiated males competed about equally with untreated males (in accordance with Knipling’s model) (Bushland and Hopkins 1953).”

#USDA (retrieved 2025): The New World Screwworm

https://www.nal.usda.gov/exhibits/speccoll/exhibits/show/stop-screwworms--selections-fr/introduction 

Quote: “The work of many people and institutions over decades contributed to the eradication effort, which now has the screwworm in retreat as far south as Panama. Throughout, research in theory and practical application by ARS scientists and laboratories made the eradication process possible. In particular, three scientists”Dr. Emory Cushing, Dr. Edward F. Knipling, and Dr. Raymond C. Bushland”performed the basic analyses and created the techniques underpinning the effort.

Cushing, in collaboration with Dr. Walter S. Patton of the University of Liverpool, established that the screwworm fly was not the same species as the more numerous blowfly, which feeds on dead animals. Following publication of this discovery in 1933, research began to focus on control of the pest. Key to the endeavor was Knipling's theory that insect pests, such as the screwworm, could be controlled by inundating wild populations with sterile males. Fertile females that mate with sterile males lay eggs that do not hatch. Reproduction would drop with each generation, eventually reaching zero if sterile flies continued to be introduced. Known as the Sterile Insect Technique (SIT), Knipling focused on ways to use it with the screwworm fly. Another element critical to eradication was in place by 1936: a way to raise large numbers of the flies for research without using live animals. At the Menard, Texas, research laboratory, Bushland developed a technique for rearing large numbers of the insects on a diet of ground meat, beef blood, water, and a small amount of preservative, such as formalin. The availability of large numbers of screwworms for laboratory research led to more effective treatment for infestations.

(...)

World War II intervened and entomologists of USDA's Bureau of Entomology and Plant Quarantine, including Knipling and Bushland, were assigned to the Orlando, Florida, station to take part in research for controlling insects that threatened U.S. servicemen and women. The rapid development of atomic research provided the fifth crucial element needed to eradicate the screwworm: a way to sterilize large numbers of screwworms, which as adult flies could compete for mates in the wild. After the war, Bushland was assigned to the Livestock Insect Laboratory in Kerrville, Texas, part of the Agricultural Research Administration, which later became ARS. Knipling directed research on insects affecting livestock and humans from headquarters in Washington, D.C. In 1950, Alfred W. Lindquist, a colleague, drew Knipling's attention to an article by the Nobel Prize winner Dr. Hermann J. Muller on the sterilization of flies by radiation. Knipling saw this as a potential solution to the problem of mass sterilization. Bushland arranged to use hospital x-ray equipment to test whether radiation could effectively and efficiently sterilize large numbers of C. hominivorax. The experiment was a success, and cobalt-60 gamma ray equipment from Oak Ridge National Laboratory made it possible to sterilize masses of screwworm flies.”

- Screwworm flies have a major weakness – Female Cochliomyia can lay up to 400 eggs, multiple times. But they only mate a single time before they die at the ripe age of three weeks.

#Šlapeta, J. (2022): Obligatory Myiasis-producing Flies of Animals. MSD Manual. Veterinary Manual

https://www.msdvetmanual.com/integumentary-system/flies/obligatory-myiasis-producing-flies-of-animals  

Quote: “Adult female flies lay batches of 200–400 eggs in rows that overlap like shingles in a mass on the edge of a fresh wound. After 12–21 hours, larvae hatch, crawl into the wound, and burrow into the flesh. The larvae feed on wound fluids and live tissue. After 5–7 days, grown larvae exit from the wound, fall to the ground, and burrow in the soil to pupate. The pupal period varies from 7 days to 2 months, depending on the temperature. Freezing or sustained soil temperatures < 46°F (8°C) kill the pupae. Adults breed only once during their lifetime, a fact that can be used as an advantage in biologic control. Adult flies usually breed when 3–4 days old, and gravid females are ready to oviposit when ~6 days old. In warm weather, the life cycle may be completed in 21 days. Only female flies feed and oviposit on wounds; males and younger, virgin females gather to breed in vegetation, especially flowering vegetation.”

#USDA (retrieved 2025): The New World Screwworm

https://www.nal.usda.gov/exhibits/speccoll/exhibits/show/stop-screwworms--selections-fr/introduction 

Quote: “New World screwworm or American primary screwworm, known now by the scientific name Cochliomyia hominivorax (Coquerel) is endemic only to the Americas. Scientists once confused C. hominivorax with the blowfly, C. macellaria, which feeds on decaying matter. Some categorized the New World screwworm as C. americana or Callitroga hominivorax before the scientific community agreed on Cochliomyia hominivorax. The life cycle of the insect lasts about 21 days in warm weather and slightly longer in cooler climates. The adult female mates only once and lays her white, elongated eggs along the edges of wounds on warm-blooded animals.”

- To prove this could work, scientists built a screwworm paradise in Florida and shipped millions of flies to the remote island of Curacao.

#USDA (retrieved 2025): The New World Screwworm

https://www.nal.usda.gov/exhibits/speccoll/exhibits/show/stop-screwworms--selections-fr/introduction 

Quote: “The Curaçao Experiment: Eradication

In early 1953, Knipling's attention was drawn by a letter from the veterinary officer B.A. Bitter on the island of Curaçao in the Netherlands Antilles, 40 miles from the coast of Venezuela. Bitter asked USDA for help treating the screwworm problem there. Curaçao turned out to be the perfect field site. It claimed a sizable population of domestic animals, it was small enough to conduct controlled field tests, and researchers believed it was far enough from South America to prevent fly migration. In 1954, screwworm flies were mass reared in Orlando, Florida, by USDA scientists and flown to Curaçao, where 400 sterile males per square mile were released by air. Effective eradication was achieved in 10 weeks.”

#Klassen, W. & Curtis C.F. (2005): History of the Sterile Insect Technique

https://link.springer.com/chapter/10.1007/1-4020-4051-2_1 

Quote: “4.1.5. Curaçao Eradication Trial — Proof of Concept In 1954, Knipling was informed that screwworms were causing severe damage to the dairy industry on the island of Curaçao, 65 km from Venezuela, with an area of only 435 km2 . Flies were reared in Orlando, Florida, and irradiated pupae were packaged in paper bags, air freighted to Curaçao, and released by air twice per week. On Sanibel, the release of 39 sterile males per km2 per week had been effective, but on Curaçao this rate caused only 15% sterility of egg masses, and it had little effect on the incidence of myiasis cases due to the presence of thousands of unattended goats and sheep. Since wounds on these animals were not treated, they supported a high screwworm population. The release rate was increased to about 155 sterile males per km2 per week, whereupon egg sterility increased to 69%, and then to 100% by the time two generations had elapsed. Subsequently two more fertile egg masses were found, and so sterile-fly releases were continued for another 8 weeks. Evidently eradication had been accomplished within 14 weeks, and the releases were halted after 22 weeks (Baumhover et al. 1955).”

- Long trays were filled with ground beef and horse meat, animal blood, milk and eggs. 

Over the decades, various types of nutrition have been experimented with. Numerous factors have played a role, above all cost and supply. Therefore, we can only give an outline of the diets of the early days here.

#Scott, M. J. et al. (2017): Review of research advances in the screwworm eradication program over the past 25 years. Entomologia Experimentalis et Applicata, Vol. 164 (3)

https://onlinelibrary.wiley.com/doi/10.1111/eea.12607 

Quote: “Components of the larval diet for mass rearing have been modified over time in an effort to reduce the cost of medium constituents and labor. Lean beef and other sources of meat used previously have been replaced with a hydroponic diet (using dry ingredients) and a bulking agent (Taylor, 1992; Chen et al., 2014). The cost of larval rearing ingredients for producing screwworms in the mass-rearing facility is about US $1.0 per 1 000 insects (Mastrangelo & Welch, 2012). Although this is an improvement over the cost of ingredients used in the past, it is still a costly endeavor. Therefore, research to improve screwworm rearing — both, improved quality of insects and improved costs — is ongoing. The use of cellulose fiber to add bulk to the screwworm larval diet in the mass-rearing facility in Panama continues to yield very high-quality screwworms, at reduced cost compared to the polyacrylamide gel used previously, and it reduces potential waste management problems (Chaudhury & Skoda, 2007, 2009). However, replacement of gel with cellulose fiber resulted in increased levels of ammonia liberated because cellulose does not adsorb ammonia; consequently, methods to reduce ammonia levels have been developed (Sagel et al., 2016). Potassium permanganate oxidizes ammonia and, when used in the larval diet, lowers ammonia levels. Further, it has anti-microbial activity, potentially serving as a replacement for formaldehyde in the diet (Sagel et al., 2016). Should regular diet components be unavailable, proposed new diet ingredients include replacing the milk product with soy flour (Chaudhury et al., 2015) or using dry blood as a source of protein for the adult colony flies (Sagel et al., 2002). When suppliers of regular ingredients undergo production changes, as occurred when anticoagulants used in the blood were changed by the supplier, these must be validated within the rearing facility as having, at worst, a net neutral effect on the quality of colony flies from the mass-production facility (Chaudhury et al., 2011). Optimization of temperature, the number of flies in a cage, and photoperiod resulted in increased egg production and reduced adult mortality (Berkebile et al., 2006) for the adult colony of the mass-rearing facility. These same optimized conditions had a positive effect on male size as well as mating competence and competitiveness (Pitti et al., 2011).”

#Chen, H. et al. (2013): Artificial diets used in mass production of the New World

screwworm, Cochliomyia hominivorax. Journal of Applied Entomology, 139(9)

https://www.researchgate.net/publication/264362943_Artificial_diets_used_in_mass_production_of_the_New_World_screwworm_Cochliomyia_hominivorax 

- Over the next few decades a war was declared and professional worm factories established to breed them by the billions.

#Chen, H. et al. (2013): Artificial diets used in mass production of the New World

screwworm, Cochliomyia hominivorax. Journal of Applied Entomology, 139(9)

https://www.researchgate.net/publication/264362943_Artificial_diets_used_in_mass_production_of_the_New_World_screwworm_Cochliomyia_hominivorax 

Quote: “Since the launch of the first eradication programme against screwworm in Florida in 1958, 1–500 million sterile flies per week have been produced on various artificial diets (Smith 1960; Goodenough et al. 1983; Whitten 1985; Taylor et al. 1991). Six screwworm facilities were built and operated for mass rearing: Bithlo (1958) and Sebring (1958–1959) in Florida; Kerrville (1962) and Mission (1962–1980) in Texas of USA; Tuxtla Gutierrez (1976–2012), Chiapas, Mexico (Graham 1985); and Pacora (2007–present), Panama, Republic of Panama.”

- A single plant in Texas alone needed 70 tons of meat and 12,000 gallons of blood to breed 150 million flies per week.

#USDA (retrieved 2025): “With Sterility Technique Screwworms Eradicated from U. S. (1966)” Special Collections, USDA National Agricultural Library

https://www.nal.usda.gov/exhibits/speccoll/exhibits/show/stop-screwworms--selections-fr/item/7353 

- This lovely process made the insects smell so bad that airlines initially refused to transport them. Their transport boxes had to be sprayed with cologne just to get them on planes.

Unfortunately, we could not find any other source than this press article. However, we found the story so cool and it sounds plausible to us (also because of the reputable source) that we wanted to tell you about it. 

#The Atlantic (2020): America’s Never-Ending Battle Against Flesh-Eating Worms

https://www.theatlantic.com/science/archive/2020/05/flesh-eating-worms-disease-containment-america-panama/611026/ 

Quote: “In the earliest days of sterile-screwworm testing, the flies stank so badly that airlines refused to ship them. Workers learned to spray the boxes with cologne.”

- Bit by bit, a slow-moving wave of biological warfare, the program eradicated screwworms. First from Florida, then across Texas, through Mexico, and into Central America.

#Hennessey, M. J. et al. (2019): Use of a multiagency approach to eradicate New World screwworm flies from Big Pine Key, Florida, following an outbreak of screwworm infestation (September 2016–March 2017). Journal of the American Veterinary Medical Association, Vol. 255 (8)

https://www.researchgate.net/publication/336565335_Use_of_a_multiagency_approach_to_eradicate_New_World_screwworm_flies_from_Big_Pine_Key_Florida_following_an_outbreak_of_screwworm_infestation_September_2016-March_2017 

#Klassen, W. & Curtis C.F. (2005): History of the Sterile Insect Technique

https://link.springer.com/chapter/10.1007/1-4020-4051-2_1 

Quote: “By 1984 the Commission had achieved the goal of eradicating the screwworm to the Isthmus of Tehuantepec (Peneda-Vargas 1985). In 1986, operations were extended to the Yucatán Peninsula and the countries bordering Mexico (Irastorza et al. 1993). Eradication was declared as follows: Mexico 1991, Belize and Guatemala 1994, El Salvador 1995, Honduras 1996, Nicaragua 1999, Costa Rica 2000, and Panama 2001, where a permanent sterile-fly barrier is being maintained in the Darien Gap along the border with Colombia (Wyss 2000; Vargas-Terán et al., this volume). A rearing facility is being constructed at Pacora, Panama, and eventually the facility at Tuxtla Gutiérrez will be closed.“

- In 1988, the war suddenly became global and for the first time ever, screwworms escaped to Africa. The stakes were astronomical - if not stopped immediately, flesh-eating Cochliomyia could move down the Nile Valley, around the North African coast and conquer regions where medical care was scarce or non-existent. The potential suffering was incalculable.

#Klassen, W. & Curtis C.F. (2005): History of the Sterile Insect Technique

https://link.springer.com/chapter/10.1007/1-4020-4051-2_1 

Quote: “In 1988, the New World screwworm was discovered at Tripoli, Libya, where it rapidly spread over 28 000 km2 . Many feared that the insect would spread throughout North Africa, the Middle East and southern Europe, and migrate up the Nile River to sub-Saharan Africa, with serious consequences for the African people, livestock, and the already endangered large mammals.”

- To stop this invasion a herculean operation was triggered immediately. Hundreds of Millions of sterile flies were flown in. Ground teams inspected millions of animals for wounds. Communication campaigns explained to locals why planes were dropping boxes full of millions of flesh eating American flies. But it worked. In just four months, the invasion was stopped.

#Klassen, W. & Curtis C.F. (2005): History of the Sterile Insect Technique

https://link.springer.com/chapter/10.1007/1-4020-4051-2_1 

Quote: “The infested area was partially isolated by the Mediterranean Sea, desert to the south, and barren areas with few livestock to the east and west. On the other hand, all of the conditions for successful overwintering and dispersal existed in a 15–25- km-wide zone along the Mediterranean coast (Krafsur and Lindquist 1996). One hundred teams, each consisting of two individuals equipped with a jeep, inspected all livestock every 21–28 days, applied insecticide to every wound, and sprayed many of the animals. About 80 swormlure-baited wing traps were deployed across the lines of flight of the aircraft from which the sterile screwworms were dropped. Sterile screwworms were supplied from Mexico — mating studies showed that the factory-strain flies were sexually compatible with the Libyan strain.

(...)

The impact of this strategy was dramatic. Only six instances of wounds infested with screwworm larvae were found in 1991, compared with more than 12 000 cases in 1990. Releases of sterile flies were continued until October 1991, and surveillance of all livestock until June 1992 (Lindquist et al. 1993). Eradication was declared in June 1992 (FAO 1992).”

- Thousands of mature flies are then carefully irradiated with precise doses of radiation, creating Cochliomyia that act normal but are dead inside.

#Bakri, A. et al. (2005): Sterilizing Insects With Ionizing Radiation. In: Sterile Insect Technique Principles and Practice in Area-Wide Integrated Pest Management.

https://www.iaea.org/sites/default/files/sterileinsecttechniquebook.pdf
Quote: “Exposure to ionizing radiation is currently the method of choice for rendering insects reproductively sterile for area-wide integrated pest management (AW-IPM) programmes that integrate the sterile insect technique (SIT). Gamma radiation from isotopic sources (cobalt-60 or caesium-137) is most often used, but high-energy electrons and X-rays are other practical options. Insect irradiation is safe and reliable when established safety and quality-assurance guidelines are followed. The key processing parameter is absorbed dose, which must be tightly controlled to ensure that treated insects are sufficiently sterile in their reproductive cells and yet able to compete for mates with wild insects. To that end, accurate dosimetry (measurement of absorbed dose) is critical. Irradiation data generated since the 1950s, covering over 300 arthropod species, indicate that the dose needed for sterilization of arthropods varies from less than 5 Gy for blaberid cockroaches to 300 Gy or more for some arctiid and pyralid moths. Factors such as oxygen level, and insect age and stage during irradiation, and many others, influence both the absorbed dose required for sterilization and the viability of irradiated insects. Consideration of these factors in the design of irradiation protocols can help to find a balance between the sterility and competitiveness of insects produced for programmes that release sterile insects. Many programmes apply “precautionary” radiation doses to increase the security margin of sterilization, but this overdosing often lowers competitiveness to the point where the overall induced sterility in the wild population is reduced significantly.“

National Academies of Sciences, Engineering, and Medicine (2021: Radioactive Sources: Applications and Alternative Technologies. Washington, DC: The National Academies Press

https://nap.nationalacademies.org/read/26121/chapter/8#110 

Quote: “Gamma rays, x-rays, and e-beams function in a broadly similar way to achieve insect sterilization: ionizing radiation disrupts normal cellular function in pests by breaking chemical bonds within DNA and other biomolecules (Barkai-Golan and Follett, 2017; Follett, 2014; Hallman and Blackburn, 2016). This damage can be direct, as electrons are removed from biological molecules, such as DNA, RNA, or proteins, or indirect, from the free radicals formed during the ionization of water molecules within the biological systems.”

- Each week 90 million flies are loaded into rotating dispersal machines to be released mid-flight in a finely tuned balance of drop rate, speed and altitude. The flight paths are separated by precisely 1.6 kilometers in an choreographed aerial ballet, creating an invisible wall of sterile flies.

The following sources refer to the program in Panama before the current outbreak (explained further below). This is an example of how complex and finely coordinated the routes and technology are. Unfortunately, we do not have any specific flight routes for the current outbreak, but we do have figures for the number of flies produced: While our consulting expert refers to 90 million flies, the program's figures go a little further (over 100 million. 

#COOPEG (2022): BIDDING FOR: “Aerial Dispersal Service of the Dispersal Center of the Panama-United States Commission for the Eradication and Prevention of Screwworm (COPEG), located at the Tocumen International Airport, Republic of Panama. (5 years)”

https://www.copeg.org/wp-content/uploads/2022/10/PLIEGO-EN-INGLES.pdf 

Quote: “B. 16 PLANE REQUIREMENTS

1. The planes shall operate in the restricted category.

2. The equipped planes shall be certified, totally in modified flight conditions of twin-engine operation capable of transport and dispersal of flies during sustained flights at speeds of 165 knots in up to 4 - 5 hours of flight time. The plane shall be able to carry out the dispersal of flies at 1,500 to 8,500 above ground level.”

#Skoda, S. et al. (2017): Distribution and Persistence of Sterile Screwworms (Diptera: Calliphoridae) Released at the Panama-Colombia Border. Journal of Economic Entomology, Vol. 110 (2)
https://www.researchgate.net/publication/315612644_Distribution_and_Persistence_of_Sterile_Screwworms_Diptera_Calliphoridae_Released_at_the_Panama-Colombia_Border 

Quote: “During all weeks of the study, 40 million sterile screwworm

flies/week were released over the barrier zone from a COPEG contracted airplane specially designed for this purpose. Flies were released so that 6,000 flies per linear nautical mile were distributed, which is the same level used for eradication.”

#The Atlantic (2020): America’s Never-Ending Battle Against Flesh-Eating Worms

https://www.theatlantic.com/science/archive/2020/05/flesh-eating-worms-disease-containment-america-panama/611026/ 

Quote: “Every week, planes drop 14.7 million sterilized screwworms over the rainforest that divides the two countries. A screwworm-rearing plant operates 24/7 in Panama. Inspectors cover thousands of square miles by motorcycle, boat, and horseback, searching for stray screwworm infections north of the border. The slightest oversight could undo all the work that came before.”

#Phillips, P. & Skoda, S. (2009): Proposal to Improve the Aerial Release of Sterile Screwworms in Panama. 

https://www.researchgate.net/publication/321225047_Proposal_to_Improve_the_Aerial_Release_of_Sterile_Screwworms_in_Panama 

Quote: “Release Strategy

The current sterile screwworm fly dispersal program in Panama uses a release rate of 6,000 flies per linear nautical mile from aircraft flying at approximately 165 knots along parallel flight paths that cover the entire barrier zone. The flight lines are based on compass bearings placed in a grid over the barrier zone that directs the aircraft (Figure 1). The current swath width ranges between 3.5 (nm) and 4.5 nautical miles (nm). This standard practice has been used by the screwworm eradication program over the years to give a dosage of 3000 flies per square nautical mile per week. The flight path grid is then shifted a mile on either side the next week to ensure a uniform application of sterile flies (Smith 2009). During the normal dispersal schedule (no outbreaks) there are 8 flights each week over the barrier zone.

Dispersal Equipment

The program uses four Beechcraft King Air aircraft each equipped with APHIS PPQ designed dispersal machines. This design has been used since 1996 (Smith 2009) with some modifications and maintenance work by APHIS PPQ over the years (Ray Penk, pers. communication). These machines are motor-driven screw augers mounted with two airconditioned release boxes that can hold approximately 230 liters each of chilled flies (Figure 2). The release rate is controlled by varying the speed of the auger and/or the aircraft. Currently the speed is monitored by the pilot and a disperser rides in the plane to monitor the flow of sterile insects out the chute of the aircraft. This has been a successful method of dispersing sterile flies throughout Central America. The systematic release of sterile flies lead to the successful eradication of New World Screwworm (NWS) fly from continental North America.”

#COPEG (retrieved 2025): Currently Situation of Screwworm in Panama

https://copeg.org/en/producer-resources/ 

Quote: “Currently, the New World Screwworm (NWS) remains in the eradication stage with incidences of positive cases in all the provinces of Panama except for the Guna Yala Region. By january 11th, Panama has a total of 24,696 positive cases, while at the regional level there is presence of NWS in Costa Rica with a total of 13,014 cases since the declaration of the outbreak, in Nicaragua there have been 9,279 cases, in Honduras 311 cases, in Guatemala 89 cases, Mexico only 3 cases, El Salvador 2 cases and Belize 2 cases of NWS to date.

The emergency response is based on three fundamental pillars:

• Increase production of sterile pupae from 20 million to 109,278,479 million per week.

• Increased aerial and ground release, with a total of 26 weekly flights in Honduras, Guatemala and Mexico that average a dispersion of more than 101,133,215 million sterile flies.

• Surveillance in field that includes visits to farms, increase in animal mobilization control posts (CMA) and increase in health education through trainings in communities, schools and farmers promoting appropriate sanitary practices.

Considering the previous points, to have better control of the worms and for the eradication measures to be effective, the active participation of producers and the population is important, promoting good livestock practices such as: inspecting, checking animals, healing the injuries, transport only healthy animals and immediately report cases of worms.”

- In 2016 Cochliomyia somehow made their way back to the Florida Keys turning the paradise islands into a nightmare. Key deer were suddenly walking around with gaping wounds. Millions of sterile flies were rushed in from Panama, creating front around the outbreak and beginning the eradication again. Within months, the invasion was at least contained. 

In the 2016/2017 outbreak, no airplanes were used but the flies were released from stations on the ground. 

#Skoda, S. et al. (2018): Screwworm (Diptera: Calliphoridae) in the United States: Response to and Elimination of the 2016–2017 Outbreak in Florida. Journal of Medical Entomology, Vol. 55 (4)

https://pubmed.ncbi.nlm.nih.gov/29722869/ 

Quote: “The authors were notified via e-mail on September 30, 2016 of a potential outbreak of screwworms on the Florida Keys. However, it was impossible to positively identify larvae in the attached photographs of Key deer (Odocoileus virginianus clavium Barboyr & Allen) that displayed suspicious myiasis (Fig. 1). Later that day, larval samples sent to the National Veterinary Services Laboratories (NVSL) were confirmed as screwworm.
(...)
We learned that from July 8 to October 6, 47 Key deer had been euthanized because of severe myiasis; the earliest suspected case in a deer occurred in early July, but was not reported. This represented a severe breakdown in reporting requirements by local veterinarians (USDA 2018). Also, some companion animals had been affected (two dogs, one cat, and one pet pig). The APHIS-VS, FDACS, and Monroe County personnel began formulating a plan to inform the local animal care facilities and institute animal movement controls. By October 4, a mandatory interdiction station, operated 24/7, was established and operating near Key Largo at mile marker 106 of the Overseas Highway to inspect all animals leaving the Keys.

(...)

The Interdiction Station closed on March 19, 2017 (having inspected >17,000 animals), and the USDA declared eradication of the outbreak on March 23, 2017 (USDA 2017). In part because of the special situation with Key deer and the “fawning” season, sterile fly releases continued in the infested zone of the Florida Keys until April 25, 2017. In all, about 194.2 million pupae were delivered to GRCs, from which roughly 188.4 million sterile flies emerged and were released (176.5 million in the infested zone, 5.5 million in the barrier zone and 6.1 million around Homestead).

(...)

Also, the first shipment of sterile screwworms was scheduled to arrive from the Production Facility in Panama on October 10.

(...)

- And in late 2023 the wall in Panama failed and Cochliomyia struck back immediately. Like a parasitic firestorm on speed it spread again all over Panama and Costa Rica. Burning through Central America and even reaching Mexiko. The worm factory now produces sterile worms at maximum capacity, it is a real biological emergency and it is not clear when it will be over.

#USDA (2025): New World Screwworm Outbreak in Central America and Positive Detection in Mexico

https://www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/screwworm/outbreak-central-america 

Quote: “In 2023, NWS detections in Panama exploded from an average of 25 cases per year to more than 6,500 cases in 1 year. Since then, screwworm has been detected in Costa Rica, Nicaragua, Honduras, Guatemala, and Mexico, north of the biological barrier that's successfully contained this pest to South America for decades.”

#COPEG (retrieved 2025): Currently Situation of Screwworm in Panama

https://copeg.org/en/producer-resources/ 

Quote: “Currently, the New World Screwworm (NWS) remains in the eradication stage with incidences of positive cases in all the provinces of Panama except for the Guna Yala Region. By january 11th, Panama has a total of 24,696 positive cases, while at the regional level there is presence of NWS in Costa Rica with a total of 13,014 cases since the declaration of the outbreak, in Nicaragua there have been 9,279 cases, in Honduras 311 cases, in Guatemala 89 cases, Mexico only 3 cases, El Salvador 2 cases and Belize 2 cases of NWS to date.

The emergency response is based on three fundamental pillars:

• Increase production of sterile pupae from 20 million to 109,278,479 million per week.

• Increased aerial and ground release, with a total of 26 weekly flights in Honduras, Guatemala and Mexico that average a dispersion of more than 101,133,215 million sterile flies.

• Surveillance in field that includes visits to farms, increase in animal mobilization control posts (CMA) and increase in health education through trainings in communities, schools and farmers promoting appropriate sanitary practices.

Considering the previous points, to have better control of the worms and for the eradication measures to be effective, the active participation of producers and the population is important, promoting good livestock practices such as: inspecting, checking animals, healing the injuries, transport only healthy animals and immediately report cases of worms.”

- In 2025 there are a few operations like this going on around the world, like in Augusta Australia, where scientists produce 40 million sterile fruit flies each week.

#Minister for Agriculture, Fisheries and Forestry (2024): One billion sterile fruit flies released over the Riverland as Port Augusta SIT facility reaches major milestone

https://minister.agriculture.gov.au/Watt/media-releases/one-billion-sterile-fruit-flies-released-over-the-riverland 

Quote: “One billion sterile fruit flies have now been released over the Riverland to combat outbreaks in the region following a recent expansion at Port Augusta’s Sterile Insect Technology (SIT) facility.

Since September the facility has doubled its production rate of sterile Queensland fruit flies (Q-fly) from 20 million a week to 40 million a week. The facility has now produced one billion SIT flies since the program started in August 2022.

The program reduces the fruit fly population by mating the sterile flies with wild flies, resulting in no fertile offspring.

The $3 million expansion was funded under the Federal Government’s $30 million Building Resilience to Manage Fruit Fly package, with additional contributions from the Department of Primary Industries and Regions, South Australia (PIRSA) and Citrus SA.

The expansion included the addition of separate rooms for each stage of the fruit fly life cycle and resulted in the recruitment of eight new staff.

Fruit flies are one of the world’s worst horticultural pest, destroying fruit and vegetables in commercial crops, home gardens and impacting on trade access.”