On August 24, the Douglas, Arizona port of entry reopens to Mexican cattle for the first time in more than a year. Santa Teresa and Columbus, New Mexico are next in USDA's phased plan. Every animal crossing gets a full USDA inspection, and the phased reopening is eventually expected to move as many as 80,000 head per month.
That inspection happens at the border. The inspection that matters on your place happens in the chute, and nobody is coming to do it for you.
New World screwworm is not a fence problem. It's a wound problem — and fences, gates, and handling equipment are the largest single source of wounds on most cattle operations. USDA's dashboard logs 44 detections since June 3, 2026. The nearest confirmed case to the US border sits a few hundred miles out. This guide is the practical version: what to look for, how often to look, and which parts of your infrastructure are manufacturing the wounds that a screwworm fly is looking for.
If you want the clinical detail — reporting procedure, sample collection, treatment protocols — go straight to the Texas A&M AgriLife Extension field guide for beef cattle producers. It is the best free resource in print and it is what this article defers to on anything medical.
What screwworm actually is, in one paragraph
The New World screwworm fly lays eggs on the edge of a wound — any wound, on any warm-blooded animal, including a scrape you'd never think twice about. The larvae hatch and feed on living tissue, which is what separates screwworm from ordinary blowfly strike. The wound gets larger instead of smaller. Untreated, the infestation can kill a mature cow in one to two weeks. Treated early, most animals recover completely. Everything below is in service of "treated early."
The five-second version: a wound that's getting worse, not better
If you remember one thing, remember that. A normal wound shrinks, dries, and scabs. A screwworm wound widens, weeps, and smells. Extension services across the Southwest have converged on the same short list of warning signs:
- A wound that is enlarging over successive days rather than closing
- A distinctive foul odor — producers who have smelled it describe it as unmistakable and unlike ordinary infection
- Visible larvae, often burrowed deep enough that you have to open the wound to see them
- Animals biting, licking, kicking, or rubbing at one spot repeatedly
- Isolation from the herd, restlessness, or lethargy — behavior changes often show up before you find the wound
- Head shaking or ear drooping, which can indicate infestation inside the ear canal where you won't see it from twenty feet away
The high-risk sites are the ones you create: navels on newborn calves, dehorning sites, castration sites, branding and tagging wounds, and any fresh laceration. Newborn calves are the single highest-risk animal on the place because the umbilical stump is an open wound by definition.
Inspection cadence: what "check them" actually means
"Watch your cattle" is useless advice. Here is the cadence Southwest extension services are recommending, translated into something you can put on a whiteboard:
- Daily for the first 5–7 days after any procedure that breaks skin — branding, tagging, castration, dehorning, calving
- Every newborn calf, daily, until the navel is fully dried and closed
- At every handling event — sorting, weighing, loading, vaccinating — look at the whole animal, not just the part you're working on
- Any animal that has been through a fence, tangled in wire, or come off a trailer with a scrape gets checked daily until the wound closes
- Any animal behaving oddly gets caught and looked at, not watched from the truck
Look in the ears, under the tail, between the toes, and at the sheath or udder. Screwworm doesn't restrict itself to the wounds that are convenient to inspect.
If you find something you think is screwworm, do not treat and move on. Contact your veterinarian or state animal health official first — reporting is how the response stays ahead of the spread, and the field guide walks through sample collection and submission step by step.
Now the fence part: your infrastructure is a wound factory
This is the part of screwworm preparedness nobody writes about, and it is the part you actually control. Every wound on your cattle came from somewhere. On most operations, a meaningful share of them came from fence, gates, or handling equipment that has been "good enough" for years.
Walk your place with this list. You are not looking for fence that's failing — you are looking for fence that cuts.
Barbed wire that's doing more than containing
Barbed wire works, and plenty of operations will keep running it. But loose barbed wire is a different animal from tight barbed wire. A sagging strand that cattle can push through, get a shoulder over, or catch a hip on produces exactly the kind of long, shallow laceration a screwworm fly wants. Tight wire gets respected; loose wire gets tested, and testing is where the cuts come from.
If you're re-tensioning, that's a job for in-line strainers and a proper tension handle rather than a come-along and hope. Our tools and hardware collection carries the crimps, tensioners and gripples that make a re-tension job hold. If you're replacing rather than re-tensioning, the barbed and smooth wire collection covers 2-point and 4-point in Class 1 and Class 3 galvanized, plus barbless twisted cable — which contains nearly as well as barbed on trained cattle without the laceration risk.
Worth reading alongside this: our comparison of fixed-knot versus barbed wire over a 30-year life. The wound-risk difference is one of the arguments that rarely makes it into the cost math and probably should this year.
Broken and protruding wire ends
The single worst offender on most places is a broken strand left twisted around a post with three inches of wire sticking into the alley. Cattle brush it every pass. Walk your handling alleys, your gate approaches, and both sides of every corner assembly, and cut off or bend back anything that protrudes. This is an afternoon with fencing pliers and it removes more wound risk than any product you can buy.
Gates and gate hardware
Gates are where cattle bunch, push, and get squeezed. Check for sharp latch hardware at shoulder height, gate frames that have bent into a point, and gaps between the gate and the post that a leg can go through. Insulated gate handles and properly hung gate assemblies are cheaper than a vet call — the electric fence gates and gate kits collection covers spring gates, one-hand handles, and complete assemblies.
The case for a hot wire in front of the barbed wire
Here's the argument worth taking seriously this year. An electric offset wire mounted 8–12 inches in front of an existing barbed or woven wire fence stops cattle before they reach the wire at all. They learn the boundary in a few days and then keep off it. Contact with the physical fence — and therefore contact-driven wounds — drops substantially.
You do not need to rebuild the fence to do this. Offset insulators mount to existing wood posts, T-posts, or woven wire, and you run one hot strand of polybraid in front of what's already there. Pair it with an energizer sized for the run — our charger sizing guide walks through the joule math, and the energizer collection covers 0.5 to 36 joules across AC, solar, battery and dual-power.
This is the cheapest wound-reduction project available to most operations, and it happens to also solve the containment problem you've been ignoring on that one stretch.
Handling equipment
Chutes, alleys, and headgates accumulate sharp edges the way everything else does. Run your bare hand — carefully — along every surface an animal contacts at shoulder and hip height. Anything that catches skin gets ground down or padded. If your handling setup is genuinely past saving, the animal management collection carries Morand chutes, alleys, and tubs.
Why this is worth doing in a week when cattle are worth what they're worth
Cattle inventory is at a 75-year low and prices have been at records. That cuts both ways on screwworm. A treated animal that recovers costs you labor and product. An animal you find late costs you a record-priced head — and if you're carrying replacement heifers you were counting on for a rebuild, the loss compounds into years, not months.
It also means a wound-prevention project that would have looked like fussy overhead two years ago pencils out easily now. One offset wire, one afternoon of cutting off broken wire ends, one gate rehung. Against the current value of a single head, the math is not close.
The two-page version to put in the truck
Every day, for 5–7 days after any procedure that breaks skin, and every day on newborn calves until the navel closes:
- Look at every animal — ears, navel, tail head, sheath or udder, feet, and any known wound
- Any wound getting bigger, weeping, or smelling foul: catch the animal
- Larvae visible or suspected: call your veterinarian or state animal health official before treating
- Behavior change with no obvious cause: catch it and look anyway
Once, this month:
- Walk every fence line and cut off or bend back every protruding wire end
- Re-tension anything sagging enough that cattle test it
- Check every gate for sharp hardware, bent frames, and leg-sized gaps
- Run a hand along every surface in the alley and chute; grind down what catches
- Price out an offset hot wire on your worst stretch of barbed wire
Bottom line
Screwworm gets into your herd through a wound, and most wounds on a cattle operation are manufactured by infrastructure you own and can fix. The border reopens August 24 with full USDA inspection on every animal crossing, which is the right control at the right place — but it is not a substitute for looking at your own cattle every day for a week after you work them.
Check daily for 5–7 days after any procedure. Check every newborn navel until it closes. A wound that's getting worse instead of better is the signal. And while you're out there, fix the wire that's cutting them in the first place.
For the clinical side — reporting, sampling, treatment products — use the Texas A&M AgriLife field guide and your veterinarian. For the fence side, browse permanent fencing, barbed and smooth wire, and tools and hardware, or read our perimeter fencing guide for the full build. Free shipping on orders over $150. Call 888-251-3934 if you want a second opinion on a stretch of fence — we've been doing this since 1994 and we'd rather talk you through a repair than sell you a rebuild you don't need.
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