Nightmare in the Meat Department (AKA: Read before eating)

Who cares, it’s not a problem in the US? It’s not a big deal, they mostly affect cattle. It’s not like it will impact us. Except it is. It’s been in the news, so let’s dive in.

New world screwworm. Just the name “screwworm” should give people some shudders, and for good reason. Like all flies, they start as a little egg. It goes downhill really fast. Because that female fly laying those little eggs…she searches out open wounds. Those open wounds could be a cut, puncture, insect bite, or even near the navel of newborns and around the eyes. Sometimes they will create their own wound, biting into the flesh of an unsuspecting mammal. Once the egg hatches, the larva goes to work. For most of our insects with complete development, the larval stage is the one that feeds and grows, while the adult stage is mostly reproduction. These larvae don’t disappoint. They crawl to that open wound and burrow in. Yep, these feed on live tissue. This is unlike other flesh-infesting flies that are primarily feeding on necrotic tissues.

Here's where it gets even worse. That name, screwworm, is because when they are disturbed, they “screw” their way deeper into the flesh. Since they are feeding on live flesh, they basically kill the flesh around the area they are feeding, causing severe damage and, in heavy cases, death to their host animal.

Still not grossed out enough? The life cycle is just 20 days, and females can lay up to 500 eggs in a very short period of time. Picture these little larvae burrowing under your skin, feeding under the skin until they pupate and pop out of you as an adult fly. You can feel them moving under the skin and some people have said you can hear little scraping sounds as they feed. Infestations have been known to kill full grown cattle.

Why are we talking about this now? Because it is spreading again, and one person recently came back into the US as an undocumented passenger. When flies infest humans, it’s called myiasis. And it’s really not a new problem. These occurred in the southern US until an eradication program started in 1954 effectively eliminated them in 1982.

This part is pretty cool; it was one of the first major pests to be controlled by the sterile insect technique (SIT). Male flies are sterilized and then released into the screwworm habitat. Since females only mate once, if they mate with one of these sterile males, they don’t lay viable eggs. As the population is reduced, fewer and fewer female flies emerge, and more and more sterile males are in the vicinity.

This process has continued over the years until the new world screwworm was pushed further south to South America, establishing a sort of border at the Panama Canal. But they are back. In 2024, screwworms were found in Mexico, heading north.

Why do we care, though? It’s in Mexico, not the US, so no big deal, right? Sure, right now, people in the US don’t have to worry about a fly laying its eggs into your body. There is a huge amount of cattle that go back and forth, and that can spread the flies. In the 1970’s screwworm in the US caused cattle producers $132 million per year. Yearly losses of cattle were estimated to be around 180,000 individuals per year.

If screwworms were to invade the US again, losses in Texas alone would top $1.8 BILLION. If you think beef prices are high now, just wait. The border has been closed to cattle and horses, when usually there are an average of 1.2 million head of cattle per year. Add to that: US cattle inventory is at a 74 year low. Hope you like pork.

To sum up:

• Flesh eating fly maggots that can build up enough to kill grown cattle.

• Meat prices potentially skyrocketing while availability decreases.

• Helping other countries with screwworm problems reduces the economic impact on the US market.

There are plenty of other flies and insects that impact people from a health and economic standpoint. If you want to beef up your fly control programs, contact us, we do that.

Lagniappe – I didn’t want to put any pictures of actual myiasis infections because it is pretty gross. So check this video out….if you dare!