What Is the New World Screwworm Fly and why the US has issued a livestock ban at the Mexico border

Time of India

a day ago

The United States has taken emergency action to suspend livestock imports from northern Mexico after detecting the alarming spread of the New World Screwworm fly, a parasitic insect that poses a deadly threat to livestock health and the American cattle industry.
This insect, which lays eggs in the open wounds of warm-blooded animals, has larvae that consume living flesh, unlike common fly maggots that feed on decaying matter.
With a newly detected infestation found just 370 miles from the Texas border, US officials fear a repeat of the devastating outbreaks of the mid-20th century that cost farmers millions in livestock losses. The US Department of Agriculture (USDA) is responding swiftly with containment strategies, including a revival of the sterile fly release program, new infrastructure, and tighter border controls.
What is the New World Screwworm Fly
The New World Screwworm is the larval stage of a metallic blue blow fly found in the Western Hemisphere. But unlike other blow flies, whose maggots feed on decaying organic matter, these parasitic maggots feed on living tissue.
According to Dr. Phillip Kaufman, entomology professor at Texas A&M University, this distinction makes the New World Screwworm particularly dangerous to livestock health. The larvae aggressively burrow into the open wounds of warm-blooded animals, including cows, horses, wildlife, and occasionally humans.
What makes the New World Screwworm Fly so dangerous
The New World Screwworm fly (Cochliomyia hominivorax) is not your average parasite. Female flies lay eggs inside wounds of animals such as cattle, deer, and even humans. But unlike typical fly larvae, screwworm maggots feed on living tissue, burrowing deeper into the flesh and causing large, infected wounds.
If left untreated, infested animals suffer from pain, severe tissue damage, and potentially death. The parasite spreads quickly and can cause outbreaks among herds, making it particularly dangerous for ranchers and livestock producers.
Additionally, wild animals can act as hosts, allowing the parasite to spread undetected.
USDA imposes emergency livestock ban to block Screwworm entry
To prevent the pest from entering the US, USDA Secretary Brooke Rollins announced a temporary halt to livestock imports from northern Mexico, effective immediately. Rollins emphasized that the USDA's early monitoring systems allowed for "quick and decisive action" to be taken. The move aims to create a barrier that halts the parasite's advance into the US, particularly into Texas, a state with a large cattle population.
Screwworm spread in the US in 1970s
The screwworm was once widespread in the US, causing enormous damage until it was eradicated in the 1970s. The breakthrough came through the sterile insect technique, where millions of lab-bred, sterile male flies were released into the wild. When these males mated with wild females, no offspring were produced, reducing the population over time.
This method worked so effectively that the parasite was completely eliminated from the US and pushed back to Panama, where it was contained for decades—until now.
How sterile flies might help to stop the Screwworm outbreak
The New World screwworm first emerged as a serious threat in the US in 1933, causing devastating losses to cattle producers, particularly in the Southeast, where damages reached between $50 to $100 million by the early 1960s. In response, the US government introduced the Sterile Insect Technique (SIT) in the 1950s—a groundbreaking method that involved sterilizing male screwworm flies using radiation. According to USA Today reports, these sterile males were released in large numbers into the wild, where they mated with wild females, resulting in infertile eggs.
Since female screwworm flies mate only once, this dramatically reduced the population.
The technique was a major success, and by 1966, the screwworm was declared eradicated from the US, at a cost of $32 million—ultimately protecting an $80 billion cattle industry. However, with the parasite's resurgence in Mexico, the USDA has launched a renewed effort. On June 18, it announced an $8.5 million sterile fly dispersal facility in South Texas, set to begin operations by the end of the year.
Additionally, the US is investing $21 million to upgrade a production facility in Metapa, Mexico, which will produce up to 100 million sterile flies weekly.
The goal is to eventually release 400–500 million flies weekly to reestablish the screwworm barrier at the Panama-Colombia border.
USDA's multi-million dollar action plan
The US is not taking chances. The USDA announced an expanding containment infrastructure and increasing response capabilities. Key elements of the plan include:
A new sterile fly breeding facility (or 'fly factory') to be built in southern Mexico by late 2025
A fly holding center in southern Texas to allow rapid deployment of sterile flies in case of an emergency
Aerial release programs targeting outbreak zones using planes to distribute sterile flies across wide areas
These measures are modeled on the successful campaigns of the past, and officials are optimistic they can contain the threat—if action is taken quickly enough.
What happens if the Screwworm Fly crosses into the US
If the parasite does breach the US border, the USDA is prepared to implement an emergency aerial release of millions of sterile flies. These would target potential breeding zones in southern Texas and other high-risk regions. Combined with aggressive surveillance and treatment protocols, this strategy is aimed at eradicating any early outbreaks before they escalate. Failure to act quickly could lead to livestock quarantines, meat shortages, and billions in economic losses making proactive containment the only viable option.
New World Screwworm Fly: Related FAQs
What is the New World Screwworm Fly?
A parasitic insect that lays eggs in wounds; its larvae feed on the living tissue of animals.
Why did the US halt livestock imports from northern Mexico?
To prevent the screwworm fly from spreading into Texas and other parts of the US
How does the sterile insect technique work?
Sterile male flies are released to prevent successful reproduction and gradually eliminate the population.
Is the infestation under control in Mexico?
Mexican officials report a decline in infected animals but the parasite has spread closer to the US border.
What is the USDA's long-term plan?
It includes border monitoring, new fly production facilities, aerial fly releases, and emergency containment strategies.
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