• Researchers launch monitoring program to prevent return of parasitic livestock fly
• Veterinary and agricultural awareness key for early detection

Researchers in California are preparing for the possible return of the New World screwworm, a parasitic fly that feeds on living tissue and previously caused widespread damage to U.S. livestock.

They are monitoring traps and educating veterinarians and farmers to stop its spread before it becomes established again.

When it previously spread, this fly caused extensive harm to livestock and took decades to eradicate.

A team at the University of California Riverside is working to prevent the return of this fly, known as Cochliomyia hominivorax, which differs from most blowflies by feeding on living tissue rather than dead animals.

The project, supported by $507,000 from California’s Department of Food and Agriculture, launches a statewide monitoring program to detect early signs of the fly’s return.

The screwworm lays eggs in open wounds of warm-blooded animals; the larvae then burrow into flesh in a corkscrew motion, giving the insect its name.

Previously common in California and the southern U.S., it was eradicated about 60 years ago using a large-scale program that released millions of sterile male flies, causing the population to collapse.

The species then moved south to Panama, where the U.S. Department of Agriculture has maintained a protective barrier.

In recent years, the fly has reappeared in parts of Central America and southern Mexico, likely aided by the unintentional movement of infected animals.

Researchers are deploying traps with bait that mimics the smell of rotting flesh to attract the fly for early detection.

The project also includes outreach to veterinarians and livestock farmers to spot early signs of infestation, as rapid intervention is key to preventing spread.

The fly poses a special threat to livestock with common wounds, such as those from barbed wire, birthing, or dehorning, and untreated infestations can worsen wounds and even cause death.

California’s dairy and cattle industries are particularly at risk due to their economic importance.

Although no cases have yet been detected in California, researchers stress public awareness as a first line of defense and advise contacting a veterinarian if unusual wounds are noticed.

The team confirms that the previous sterile fly technique remains the most effective method if a new outbreak occurs.

In rare cases, humans can be affected, particularly if wounds are left untreated, but livestock remain the main concern.

Researchers emphasize that the program aims for preparedness and vigilance, not fear, highlighting the importance of monitoring for signs of infection and taking preventive measures immediately.