Screwworm are here.

[acem]

There are now 5 confirmed cases of new world screwworm in the US. 4 in Texas, 1 in New Mexico.

They are on the move.

 

[Rawleigh99]

Will Ivermectin kill them?

[Lazy WP]

They have been so focused on getting the sterile flys out, that they forgot the basics. 
I truly believe this is another shot at production agriculture. They can’t control livestock people because of their independence, so they allow a very invasive species in, then quarantine herds that don’t conform to the ideals! 
Sorry Ace, I probably just got this poofed 

[Lazy WP]

5 hours ago, Rawleigh99 said:

Will Ivermectin kill them?

https://www.facebook.com/share/1CLNBVEQEt/?mibextid=wwXIfr

[acem]

Ivermectin has some effect on the larvae (worms) while it's in it's host animal but dewormers are not effective  at controlling the spread. They can use any animal (including birds) as a host which means we cannot control them just by treating livestock and pets. Rats, deer, cougars, birds, even people are good hosts and carriers. They migrate easily on hosts and with other carriers.

Actually the story of how this happened is more interesting.

Screwworms are the larva stage of a fly very similar to a house fly. The flies lay eggs in living flesh, preferring open wounds and soft, moist flesh. The eggs hatch into larvae (maggot) and eat their way through flesh until they reach the stage to exit the body, drop into the soil and pupate into a fly to repeat the cycle. Flies continue to lay eggs in the would/flesh. Without treatment The host animal typically dies within two weeks from damage to an organ or artery/vein.

Untill the mid 1900s, screwworms were endemic (native) to north America.They overwintered in south Texas, Florida,  near the gulf coast, and the areas of the southwest that have warm winters. They move northward in the spring similar to army worms. During the summer and fall they were common in the southern US sometimes migrating much farther north

For decades screwworms were pushed south, out of north America then central America through the use of sterile flies. They remained endemic  in South America.  The Darien Gap was a natural barrier with little movement of people and animals. One smaller sterile fly production facility was maintained to keep south Panama supplied with sterile male flies to fight outbreaks in southern Panama.

Then the situation changed causing the system to fail.

Several years ago large groups of people began travelling up through the Darien gap and northward through central America and Mexico into the USA. Some of these migrants became infected with screwworms in south America or the Darien gap and carried them north through the gap and north. They carried the larvae north of the sterile fly area. Animal and Livestock movement within central America and Mexico has also aided the spread since the jump across the Darien gap and southern Panama.

The remaining sterile fly production facility has not been able to keep up with the movement of screwworms with the new vector. Additional production facilities are under construction but it takes time.

Most entomologists expected screwworms to enter the US last summer but luckily they did not. 

Now that they have crossed the border it will be difficult to control their spread with our highly mobile culture.

Here's an example to consider 

Nick starts hauling dry van trailers. He picks up a load of car parts in a screwworm area. Then he hauls it to Detroit. A hundred screwworm flies exit his trailer when they open the doors before backing up to the dock. They leave the trailer and find dogs, cats, rats, birds, etc to infest and spread. Nobody in Detroit is looking for screwworms so they go unnoticed. A few weeks later they have spread across the entire great lakes area (they probably won't thrive near lake Superior with the cool temps).

[766 Man]

17 minutes ago, acem said:

Ivermectin has some effect on the larvae (worms) while it's in it's host animal but dewormers are not effective  at controlling the spread. They can use any animal (including birds) as a host which means we cannot control them just by treating livestock and pets. Rats, deer, cougars, birds, even people are good hosts and carriers. They migrate easily on hosts and with other carriers m.

Actually the story of how this happened is more interesting.

Screwworms are the larva stage of a fly very similar to a house fly. The flies lay eggs in living flesh, preferring open wounds and soft, moist flesh.

Untill the mid 1900s, screwworms were endemic (native) to north America.They overwintered in south Texas, Florida,  near the gulf coast, and the areas of the southwest that have warm winters. They move northward in the spring similar to army worms. During the summer and fall they were common in the southern US sometimes migrating much farther north

For decades screwworms were pushed south, out of north America then central America through the use of sterile flies. They remained endemic  in South America.  The Darien Gap was a natural barrier with little movement of people and animals. One smaller sterile fly production facility was maintained to keep south Panama supplied with sterile male flies to fight outbreaks in southern Panama.

Then the situation changed causing the system to fail.

Several years ago large groups of people began travelling up through the Darien gap and northward through central America and Mexico into the USA. Some of these migrants became infected with screwworms in south America or the Darien gap and carried them north through the gap and north. They carried the larvae north of the sterile fly area. Animal and Livestock movement within central America and Mexico has also aided the spread since the jump across the Darien gap and southern Panama.

The remaining sterile fly production facility has not been able to keep up with the movement of screwworms with the new vector. Additional production facilities are under construction but it takes time.

Most entomologists expected screwworms to enter the US last summer but luckily they did not. 

Now that they have crossed the border it will be difficult to control their spread with our highly mobile culture.

Here's an example to consider 

Nick starts hauling dry van trailers. He picks up a load of car parts in a screwworm area. Then he hauls it to Detroit. A hundred screwworm flies exit his trailer when they open the doors before backing up to the dock. They leave the trailer and find dogs, cats, rats, birds, etc to infest and spread. Nobody in Detroit is looking for screwworms so they go unnoticed. A few weeks later they have spread across the entire great lakes area (they probably won't thrive near lake Superior with the cool temps).

  Good clear concise explanation. 

[acem]

If you want to blame the government there's a good case for blaming certain groups encouragement of immigration, causing the vectors through the Darien gap.

However screwworms are native to the US and New World. They were not developed in some lab like The Boys From Brazil 

[Drysleeves]

Just another benefit to open border policy.

[acem]

Sale barn operating 15 miles from first screwworm case.

https://www.agriculture.com/texas-sale-barn-adapts-after-first-u-s-new-world-screwworm-case-in-decades-11994527

[ryangpayne]

Found this in an old barn recently. As a rancher in west central TX I dread dealing with them but my dad and grandpa dealt with them in the past and just as they did, we will do everything we can to protect our animals. 

[ray54]

I remember having an out break late summer early fall in 74 I think it had to be. Cattle were on barley stubble about 10 miles from home. No corrals at the place, calving started in Oct. I want to say only one or two cows needed treating. More in calves in the navel. Much easier to handle on the end of a rope. My dad always had 2 or 3 good horse to rope cattle out in the open. About a 1/3 of the cattle belonged to friend that live next door to the stubble. He was not the cowboy dad was, but they managed to keep them all doctored.

 

I was in college only around maybe 3 days a week. I don't remember roping any. Just getting sit on and hold some calves down. In this part of the world KRS wound dressing was still the old reliable. A tar past with a very distinct smell. I believe a new spray can version might have been around. I remember putting spray or liquid on the wound and worms would come crawling out. Also poking with knife or bale wire maybe dragging eggs out that did not crawl yet.

I don't think we got an early freeze, but cooler weather slows them down. Maybe release of sterile fly's. By winter when the cows came off stubble it was over. This farmland had several miles of common boarded with a 100,000 acre military base.  Maybe the government brought those up from Central/South America and that is why they were not that wide spread. But the 101 highway from LA to SF is only 2 miles away too.

[acem]

1 hour ago, ryangpayne said:

Found this in an old barn recently. As a rancher in west central TX I dread dealing with them but my dad and grandpa dealt with them in the past and just as they did, we will do everything we can to protect our animals. 

I remember something like that but thought it was purple?

Smelled strong.

[Lars (midessa)]

Years ago, in the late 70’s early 80’s I recall seeing what we called ‘grubs’ on the the very top of the backs of some of the dairy cows. They were burrowed just under the hide. We could stand right next to the cow while milking(yes, we milked in a stantion barn, we squeezed the bump and the ‘grub’ would pop out. 

[IH Forever]

15 hours ago, acem said:

I remember something like that but thought it was purple?

Smelled strong.

As a kid my Dad and about 200 head of ewes. I do remember him spraying  something purple on sheep if they had a sore or on their back side when they had the scours. Don’t know if it made it this far north but remember him saying it was for screw worm.

[ray54]

5 hours ago, Lars (midessa) said:

Years ago, in the late 70’s early 80’s I recall seeing what we called ‘grubs’ on the the very top of the backs of some of the dairy cows. They were burrowed just under the hide. We could stand right next to the cow while milking(yes, we milked in a stantion barn, we squeezed the bump and the ‘grub’ would pop out. 

That would heal fly in the larva stage. The larva under the skin were called warbles here. I don't think they where a real health threat, but cannot say for sure. Horses could get them too. Generaly tried to not ride one with a warble in the saddle area. To deal with them dad started using the first pour on insecticides on cattle in the late 60's. Don't hardly ever see a warble today.

[SASW6]

1 hour ago, ray54 said:

That would heal fly in the larva stage. The larva under the skin were called warbles here. I don't think they where a real health threat, but cannot say for sure. Horses could get them too. Generaly tried to not ride one with a warble in the saddle area. To deal with them dad started using the first pour on insecticides on cattle in the late 60's. Don't hardly ever see a warble today.

As I remember they were good sized grubs. We did the same thing stand their wile the milker was on and squees them out.

[acem]

I read screwworms start at the surface and dig in through flesh until they are ready to pupate and exit the body.

[acem]

Up to 11 cases. Almost half way up Texas already. Seems to be moving awfully fast...

They may get here this summer. 

Texas is the nation's largest beef cattle state with lots of cow calf, stockers/backgrounding and feedlots. I don't see how this cannot effect the cattle markets. 

Quarantines are going up.

Here's a historical map showing overwintering areas with the extent of the 1951 and a montage of images from the USDA.

 

[Jacka]

On 6/11/2026 at 11:37 AM, Lars (midessa) said:

Years ago, in the late 70’s early 80’s I recall seeing what we called ‘grubs’ on the the very top of the backs of some of the dairy cows. They were burrowed just under the hide. We could stand right next to the cow while milking(yes, we milked in a stantion barn, we squeezed the bump and the ‘grub’ would pop out. 

When I started milking i bought a bunch of Jerseys from a large dairy near me.They pasture a lot of their cows.I would say at least 90% of the cows i bought had warbles.They had them for several years. They would get to their back and I would squeeze them out when milking and put them in a container of bleach.They disappeared after several years of this hand eradication. They didn't reproduce that fast I guess.Really wasn't a big deal,only had one cow that kinda was sore until I sold her years later.I also remember in the 70's giving screw worm medicine to calves in their navel. I don't know if they had them but I remember doing in it. It's that same nasty smelling stuff pictured on here in a previous post

[acem]

Online screwworm training from Texas A&M extension.

https://agrilifelearn.tamu.edu/s/product/new-world-screwworm-preparedness-and-response-education/01tQn00000H7J5lIAF

[acem]

Texas may use Slormlure. It's a fly bait with insecticide.

https://texasagriculture.gov/News-Events/Article/10470/TEXAS-AGRICULTURE-COMMISSIONER-SID-MILLER-AND-USDA-TO-DEPLOY-SWORMLURE-5-IN-AGG

Below is a vintage video from when it was developed in the 80s.

 

https://www.nal.usda.gov/exhibits/speccoll/exhibits/show/stop-screwworms--selections-fr/item/6902

[acem]

Vintage sign.

[acem]

Some good history on the screwworm.

 

https://www.drovers.com/news/new-world-screwworm-u-s-eradication-resurgence

https://www.nal.usda.gov/exhibits/speccoll/exhibits/show/stop-screwworms--selections-fr/1976-1980

 

[acem]

Total confirmed cases are now 15. All reports so far are in domestic animals, mostly cattle and sheep.

There are Quarantines in 10 counties.

 

[acem]

Up to 20 cases. All domesticated animals. 

South central Texas counties  are filling in with cases. 

Arkansas, Louisiana and Oklahoma will likely get some by late summer, in my opinion.

Here's a map and link to an article.

https://www.drovers.com/news/how-far-could-new-world-screwworm-spread-summer