Every cattle producer knows that pests are a challenge to our operation, but some pests are far more dangerous than others. One of the new threats to our herd comes from the New World screwworm, which is currently advancing through Central America into southern Mexico and could soon be at our border.
The New World screwworm is a fly that has a particularly gory way of harming our cattle. Female screwworm flies lay their eggs in open wounds or body orifices and when the larvae hatch, they burrow deep into the skin like a screw driving into wood. These maggots feed on cattle’s tissue, causing larger wounds as they go.
Flies and their burrowing larvae cause extensive damage to cattle and infestations can spread rapidly. In 1966, we eradicated screwworms in the U.S. through sterile insect technique. The USDA bred sterile male NWS flies that mated with wild female screwworms and failed to produce offspring. Eventually, these flies died out in the U.S. and now they only exist in a handful of South American countries.
Unfortunately, these flesh-eating flies are now on the march north.
Since 2022, USDA’s Animal and Plant Health Inspection Service (APHIS) has confirmed the presence of New World screwworms in Costa Rica, Nicaragua, Honduras and Guatemala. Just last month, screwworms were discovered in southern Mexico.
Once in Mexico, it is easy for screwworms to travel north and appear on our southern border. These flies can hitch a ride on people, livestock, or wild animals, not to mention the thousands of vehicles and cargo containers traveling through Mexico to the U.S.
We know how devastating it would be if New World screwworm returned to the U.S., which is why the National Cattlemen’s Beef Association (NCBA) is raising the alarm now. First, we are communicating with Mexico’s cattle industry leaders so they can begin the process of screening for these flies and push for eradication efforts in their country. We are also supporting USDA’s APHIS to bolster the use of sterile flies. Recently, we have been concerned that our existing sterile flies might not be getting the job done, and NCBA is pushing for more flies and better flies that will help us beat back these pests.
Although we haven’t confirmed any New World screwworms in the U.S., we need you to be on high alert. New World screwworms have orange eyes, a metallic blue or green body, and three dark stripes across their backs. If you see any suspicious flies, please alert your local veterinarian, extension agent, or contact APHIS Veterinary Services.
Please also pay close attention to your cattle and watch for any open wounds or sores. If cattle exhibit irritated behavior, head shaking, you notice the smell of decaying flesh, or spot maggots in a wound, seek treatment from a veterinarian immediately. Proper wound treatment and prevention is the best way to protect your farm or ranch from a screwworm infestation. NCBA is also sharing the latest updates through our website. I encourage you to visit www.ncba.org/NWS for all the latest information on how to protect your operation.
NCBA is always on the clock to protect the U.S. cattle industry from threats like New World screwworm. Through your vigilance and NCBA’s advocacy, we can protect the U.S. cattle herd. — Kim Brackett, NCBA policy division chair
