The flies released by the Americans are called New World Screwworms, a species of fly originating from the Americas. This type of fly lays its eggs in the wounds of large animals. Once hatched, the larvae will directly feed on the blood from the wounds, causing the animal to become ill or even die, significantly impacting livestock farming.
The scientific name for this fly is C. hominivorax (screwworm fly). In Latin, *hominis* means “human” and *vorax* means “to eat.” Therefore, if translated directly, the name of this fly would be the “human-eating fly.” This species can indeed parasitize humans. In 1858, a large-scale outbreak of a contagious disease in humans occurred due to the larvae of the screwworm in a French prison in South America.
This species can indeed parasitize humans.
The C. hominivorax fly, also known as the screwworm fly, New World Screw Fly, is a dangerous parasitic fly species native to the Americas. They are notorious for their larvae (maggots) that can consume the living tissue of warm-blooded animals, including humans.
The larvae of this fly have long plagued the southern United States, causing significant economic damage to the livestock industry each year. Subsequently, a scientist named Edward Knipling devised a method to eradicate this fly. After a long period of observing the C. hominivorax flies in the laboratory, Edward Knipling discovered an important characteristic: the females of this fly only mate once in their lifetime (the lifespan of this fly is only about three weeks).
This led Edward Knipling to a brilliant idea: if sterile male flies are released into the wild, the females will not lay eggs after mating and will not harm other animals. Moreover, if sterile males are continuously released into the wild, the number of male flies will gradually decrease from generation to generation. In other words, this fly species can be eliminated by releasing a large number of sterile males into the wild over time.
Females of this species only mate once in their lifetime.
Adult flies are approximately 8-10 mm long, with a metallic blue or green color and black stripes on their thorax. The flies lay eggs in open wounds, the navels of newborn animals, or openings on the human body. The eggs hatch within 24 hours, and the larvae then consume the living tissue of the host, causing severe damage and even death. C. hominivorax is a primary cause of myiasis in both animals and humans. Myiasis can lead to symptoms such as pain, swelling, necrosis, and septicemia.
In the 1940s, this was considered a ridiculous idea, and Edward Knipling didn’t even dare to request funding for this research topic, so he could only use surplus funds from other projects for his studies.
Edward Knipling began experimenting with irradiating male flies with various doses of X-rays in the laboratory. This process required extremely precise control. If the radiation was too weak, it would not be sufficient to sterilize the male flies, while if it was too strong, it would make them unattractive to females. After many trials and errors, he mastered the precise parameters that could render the male flies sterile.
In 1954, Edward Knipling’s team tested their method on a small island in the Caribbean and successfully eradicated this fly species from the island. In 1957, the U.S. Department of Agriculture began using Edward Knipling’s method to eliminate screwworms in Southern states by continuously releasing lab-reared sterile males into the wild.
This species used to appear in the southern United States, Mexico, and Central America, but has been successfully eradicated through pest control programs.
In 1966, the U.S. government declared that all screwworms had been eradicated in the country.
Although there are no screwworms in the U.S., it has been observed that they can still fly in from Mexico, so the U.S. must continue to release sterile males along the U.S.-Mexico border. As you can see on the map, there is a long land border between the United States and Mexico, stretching over 3,000 km. Continuously releasing flies along such a long border is very costly. Therefore, the U.S. and Mexico discussed a plan – the U.S. government would help Mexico eliminate the screwworms, and once completed, the U.S. would only need to release sterile males along the narrow land border in southern Mexico.
By 1991, the U.S. government had assisted Mexico in eradicating the screwworms. Following this, Americans began collaborating to eradicate screwworms with Central American countries, moving through Belize, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica, and Panama. Ultimately, in 2002, they conducted eradication efforts up to the borders of Panama and Colombia. The width here is only 300 km, making it easier to maintain the elimination of screwworms.
The U.S. Department of Agriculture and the Panamanian Ministry of Agriculture jointly established an organization named COPEG. The full name of this organization, if translated into Vietnamese, is “Panama-U.S. Commission for the Prevention and Eradication of Screwworms.” However, in practice, you only need to look at the organization’s LOGO to understand its function.
Every week, COPEG breeds millions of sterile male flies in the laboratory and then releases them by airplane into the tropical rainforest at the border of Panama and Colombia to continue preventing the screwworms.
