The New World Screwworm (NWS) is so terrifying that its Latin name, Cochliomyia hominivorax, literally means man eater. But despite its fearsome reputation, few people today know about or remember the scourge that these flies were in rural areas stretching from Florida to California and southward to the Panama Canal.
The NWS is known for laying thousands of tiny eggs, between 200 and 500 per clutch, in open wounds on mammals. When these eggs hatch, they disgorge hundreds of tiny worms, which then dig into the exposed flesh. The infection is incredibly painful. Any attempts to remove the worms often result in them digging (or screwing, hence the name) deeper into the flesh. As you can imagine, having hundreds of tiny worms feasting on your flesh is painful, and if left untreated, the results can be deadly.
Screwworms are so dangerous because one infestation can breed hundreds of flies, which go on to lay thousands of eggs in surrounding animals. Screwworms are not picky about their hosts. They will tear into the flesh of cattle, squirrels, deer, dogs, and even humans, infecting them. Cattle were long the favored host for these worms, and they feasted on the large populations of cows in the Southern United States and Mexico. Old time ranchers will still be able to tell you horror stories of calves writhing in pain before dying and having hundreds of dreaded New World Screwworm Flies pour out of the corpse.
The Latin name, again, meaning man eater, came from a particularly nasty infestation in South America. An island prison known as Devil’s Island was home to thousands of these awful flies, and they killed hundreds of people over a period of years. Not only do the flies lay eggs in wounds but the larvae also eat the flesh itself. The presence of the screwworms in a wound prevents the wound from healing, and the eating of the flesh by the worms causes them to enlarge and remain open, which invites infection and death.
For decades, between 1900 and 1950, millions of dollars in cattle were killed by screwworms. Infestations could devastate ranches and lead to massive losses in productivity. The worms were especially devastating to calves and pregnant mothers. The flies would often target mothers who had just given birth and the freshly born calves. A single barbed wire cut could invite death through infestation. These worms were a plague on rural and remote ranches for decades. Many had resigned themselves to the fact that attacks by screwworms were just a part of life on the American frontier. However, the invention of specialized radiation devices gave people hope that the bugs could be combated and eventually eradicated.
In order to rid the world of these nasty parasites, a concentrated effort was launched in 1957. The program is still in existence today. Through a process of spreading infertile screwworms, the USDA, along with a host of international partners, have pushed the screwworm out of the United States and down the spine of Central America. Today, an invisible barrier exists between Panama and Colombia, which prevents screwworms from reinfecting North America, and that barrier is upheld by millions of tiny worms that are dropped from planes on a near-daily basis.
The method that the USDA invented to control the screwworm population in North America involves breeding millions of these horrifying bugs in specialized labs. During a very specific point in the flies’ development, they are hit with a burst of radiation, which leaves them infertile and unable to mate. The infertile bugs are then loaded into boxes, put into planes, and then dropped from the air. The mass numbers of sterilized insects outcompete their fertile companions, leading to a severe drop in reproductive activity. As a result, the flesh-eating larvae of these bugs cease to exist.
This effort is spearheaded by the USDA in partnership with the Comisión Panamá–Estados Unidos para la Erradicación y Prevención del Gusano Barrenador del Ganado or COPEG. COPEG is based in Panama and they run the labs and oversee the flights of the sterilized insects. Flights are launched every other day, typically on Mondays, Wednesdays, and Fridays. These flights drop an estimated 14.7 million sterilized bugs over the jungles of Southern Panama every week.
On its face, this plan seems harebrained and like an exercise in government graft and overreach, but in this case, the program actually works. Insect sterilization has a number of benefits. It is cheap, it does not introduce genetically engineered or modified insects into the population, it does not disrupt the natural environment (where screwworms are native), and it does not affect the living mammals targeted by the screwworm larvae. Old attempts to control screwworms often involved invasive pesticides or harmful chemicals, which affect the hosts as much as it did the insects themselves.
(This method differs from similar projects aimed at reducing the number of disease-bearing mosquitoes, which involve the use of genetically modified mosquitoes. The idea of releasing millions of genetically altered mosquitoes has caused concern among many people. Insect sterilization does not suffer from the same negative public perception.)
This program costs millions of dollars each year, so there is a chance your tax dollars have been used to fund this program. Your money could have helped put gas into the planes, dropping millions of screwworms over the jungles of Panama.
I asked my wife about this project. She’s a veterinarian who did a brief internship at the USDA. She rolled her eyes and told me not to bring the project up in front of any USDA employees. Apparently, their pride in this program borders on unsufferability. And why not? Their crackpot scheme actually worked, and thanks to their efforts, American youth no longer know about the horrors of the New World Screwworm Fly.
And that is why the United States drops millions of flesh-eating worms onto Central America every week.
