As the NWS has made its way back into the lower United States, concerns grow for not just cattle ranchers, but all farmers, horse owners, and pet owners. Really anyone with animals that have extended time outdoors have to watch out for NWS! If you don’t know what New World Screwworm is; “New World screwworm (NWS), or Cochliomyia hominivorax, is a species of parasitic fly that completes part of its lifecycle by feeding on the tissue or flesh of warm-blooded animals and people. NWS flies are attracted to wounds and body openings like the nose, eyes, ears, and mouth, where they lay eggs. The eggs hatch into maggots (larvae) that eat live tissue, causing a worsening, often painful and foul-smelling wound. - CDC https://www.cdc.gov/new-world-screwworm/about/index.html “ New world screw worm is a problem, but it can be combated. Even more good news! The country has already taken measures to ensure its eradication again!
What is the country doing to prevent the spread of NWS?
We got rid of NWS once already and unfortunately it’s back. The largest attribute to the success of eradication was the use of sterile male flies. NWS has a weakness in the fact that female flies will only mate once in their life. If they do so with a sterile male fly there is no offspring, when this is done over the course of aprox. three to five generations you have a high chance of complete eradication! February, 2026 was when the US released its first batch of sterile flies. They have since released 142 million sterile flies over the course of one to two generations thus far.
What does this mean for you?
Be proud that you are a part of a country that is proactive in protecting you and your livestock. The fight against NWS in our country is not over, but it certainly is moving in a positive direction! You are likely to still experience NWS activity either through non sterile flies, but mostly through sterile male flies. The population of NWS flies in the US was low to start off with and only 32 confirmed cases have been reported since its re entry. Adult NWS flies don’t impact us much differently than a common house fly. In case you are wondering if NWS flies bite, they do not. The larvae are the main issue. Regular fly control products do work just the same on NWS flies. It also is highly unlikely that you will see any shortages in fly control products as well . The CDC does not say that over use of control products will help anything, and actually is considered more dangerous due to overdosing animals rather than helping.
So what can you do?
Be clean! More than anything, don't give a home to any fly. Keeping the same application rates of fly control products that you have been doing in the past will continue to be sufficient for the current landscape of the NWS situation. Learn how to identify! NWS flies have a metallic blue or green body slightly larger than a housefly, large orange/reddish eyes, and three dark vertical stripes on its back (the middle stripe is shorter)
New World Screwworm fly:
Common Fly:
Bot Fly:
The fly is commonly mistaken for the NWS fly they both have a bright metalac looking body however the bot fly is much larger than the NWS fly and has much darker colored eyes. If you are sure that you have encountered a new world screwworm fly contact your state's department of agriculture.