New World Screwworm Hopefully all livestock producers are beginning to pay attention to recent headlines concerning the New World Screwworm (NWS). If you have been dismissing this threat, you stand the chance of losing livestock and income. The screwworm was originally eradicated in the U.S. in the 1960’s. It had been contained to South America but began migrating northward and was detected in southern Mexico in November 2024 and just very recently in northern Mexico, just 70 miles from the Texas border.
How is it different from other blow type flies? The name screwworm refers to the feeding behavior exhibited by the maggots as they burrow (screw) into the wound. These maggots and their feeding cause extensive damage by tearing at the hosts’ tissue with sharp mouth hooks. The wound will become larger and deeper as more eggs hatch and larvae feed on the living tissue. This results in serious and often deadly damage to the animal if not discovered and treated promptly.
How worried should you be about the NWS? I would certainly be diligent and work towards being ready for a potential infestation possibly as early as next year. Once it gets here, we will be dealing with it for several years. Here are some of the most suggested and practical steps you can take to help combat against the pest. Calving, lambing, and working cattle during the colder months while the fly is inactive will be critical. Some specialists worry we may lose the bulk of our summer calf crop due to naval infestations. Birthing will require extra precautions at any time of year, but especially in the warmer months. The screwworm fly will be more active at temperatures above 60 degrees, with no-fly activity when temperatures fall consistently below about 45 degrees. Just think about when you see house flies and other fly activity; it is when the temperatures warm up, the screwworm will be no different. Changing calving, kidding, or lambing seasons will not be overnight, but it is something to consider working towards for the next birthing season.
Other things you can do to be prepared are to ensure your working facilities are up to snuff. You will need facilities where you can easily catch your livestock as needed for treatment and inspection. You will want to train your cattle to come to cake, perhaps feeding them in a trap that will lead to your working facilities. If you had rather not feed, then have a system where they have to move through a central trap when changing pastures. Whatever you do, you will have to be able to catch your livestock more easily and more regularly than you have in the past. The days of only seeing your animals once a week or even a month are over.
There are already effective products for treating the screwworm and more are being approved as we go, but these products must be applied to the wound or naval. There are no systemic treatments that are effective. In other words, you cannot give your animals a shot, drench, or bolus and expect it to keep the screwworm flies away from open wounds. This is when it will be necessary for you to catch and treat the suspect animal and hopefully be able to catch and retreat them.
The only way to eradicate the screwworm again is with sterile flies and we are a few years away from having the facilities completed that will produce enough flies to be able to do this. You will not be able to wait for a magic bullet, treatment, or medication to protect your herds and flocks. It is going to take boot leather and some preparations. Most of us probably need to update our working facilities and our cattle prices are high, so it is a good time to go ahead and make those improvements. I do hate calving and especially lambing in the winter when there is a chance of a bad cold spell, but I am afraid that is going to be necessary or stand the chance of losing a portion of the year’s crop.
Inspection and reporting are going to be of major importance in helping to track the movement and spread of the pest. Please if you think you have an animal with screwworms, isolate and treat them and call your veterinarian or Texas Animal Health Commission. There are no penalties or harsh scrutiny if you are found to have the screwworm, but it is imperative that we be able to locate and track their movement.
Texas A&M AgriLife Extension has some good fact sheets and informationyou are welcome to come by the office for the flyers, or you can locate additional information from the QR code on the image below. We also have an excellent beef program scheduled for Oct. 30 from 10 a.m.- 2 p.m. at The Station FNB (815 North Patrick, Dublin, TX) that will cover the screwworm and other current issues for beef producers. Red Chain Feeds will provide a good lunch so if you are interested in attending, please give us a call to RSVP (325)-356-2539.