7 reasons flesh-eating screwworms are as gross as you think

Flesh-eating screwworms have infested a larger portion of the Florida Keys than previously thought, according to a joint announcement Tuesday by the U.S. Department of Agriculture and Florida Department of Agriculture.

Two weeks ago, this blow fly and its parasitic maggots were thought to be contained on two islands — Big Pine Key and No Name Key — causing the state to issue an agricultural state of emergency. Adult screwworms are now infesting islands of Middle Torch Key, Little Torch Key, Cudjoe, Ramrod and Summerland. Officials said close to 100 deer in the Florida Keys have died. A dog, feral cat and pig have also tested positive.

Nearby states have started taking precautions. Robert Cobb, Georgia’s State Veterinarian, has banned the import of animals from the quarantined area in the Florida Keys unless a special permit is issued.

“Please make yourself familiar with Screwworms and how they present in animals. Be alert.” Cobb said in a statement. “This can rapidly cause serious illness and even death.”

So, here’s what you need to know about these buggers, just in case this festering outbreak continues to grow.

1. Last time the U.S. had a screwworm outbreak, ‘Eye of the Tiger’ topped the Billboard charts

The last reported case of screwworms in the U.S. was reported on August 30, 1982 in Starr County, Texas. Florida’s ongoing outbreak is the state’s first in half a century.

“It’s an age thing,” Texas A&M livestock and veterinary entomologist Sonja told PBS NewsHour. “Anybody under the age of 40 knows nothing about this screwworm unless you went to school to learn about bugs.”

2. Two screwworms roam this Earth, one worse than the other

There are two types of screwworm flies: Old World (Chrysomya bezziana) and New World (Cochliomyia hominivorax). “Hominivorax,” by the way, means “man-eater.”

Old World screwworms are present throughout Africa, Southeast Asia and several countries on the west coast of the Persian Gulf. Meanwhile, the New World species sticks to the western hemisphere. They have similar parasitic needs and nearly identical lifecycles.

A New World screwworm is the maggot of Cochliomyia hominivorax blowflies. Here, a sterile male screwworm fly is marked with a numbered tag to study fly dispersal, behavior, and longevity. Photo by Peggy Greb/U.S. Department of Agriculture

However, New World screwworms, such as those in Florida, outmatch their Old World cousins by laying more than one clutch of eggs at a time. In fact, New World flies can lay six to eight batches or more into a wound. Deaths appear to be more common with New World than Old World screwworms.

New and Old World screwworms are the only flies that consume live flesh as a primary food source, Swiger said, and the closest alternative in this regard is botflies.

But botflies create a wound with a small number of eggs to avoid killing their host. Once botfly maggots mature into adults, they take off. Screwworms, in contrast, will live inside an animal until it is deceased.

3. Flesh-munching screwworms attack humans, but we’re Plan B on the menu

Humans can catch screwworms in the same manner as other warm-blooded animals. Mother screwworm flies are attracted by the smell of open wounds. Upon finding one, the fly lays its eggs, which hatch and go to work.

The maggots’ powerful jaws slice through tissue, allowing the larvae to dig close to two inches into a wound. Little spines on the outside of the screwworm anchor into the tissue, making the creepy crawlers hard to remove.

Aside from open wounds, screwworms can invade mucus-covered tissue — like that in eyes, ears, nostrils and the anus. The buggers can also squirm into the belly buttons of newborn mammals.

The screwworms then expand their feeding area from skin into deeper tissue, such as muscles. The larvae eventually crawl out of an animal and fall to the ground, where they mature into adult flies An infestation of screwworm maggots on a human body is called myiasis.

So far in Florida, livestock and house pets have tested positive for screwworms, but no humans.

In fact, human infestations, in general, are rare. “It is actually very rare for screwworms to infest humans. We’re their last choice usually,” Swiger said. If left untreated, myiasis can be fatal, but that’s also an uncommon outcome for humans.

4. Screwworms are tricky to treat, so cover those wounds, especially with pets

Here’s what you should do in the unlikely event that you, a friend or a pet catch screwworms.

No medications are available, at least none approved by the FDA. Therapy options are limited to surgical removal of the pests and antibiotics to prevent secondary infections by other germs.

“With pets, you could go to a vet and help remove maggots but we do not have that option with wild animals,” Dr. Swiger said.

Ranchers can tend to tackle livestock infestations by rubbing approved insecticides into the wound, which is followed by pulling out individual larva with tweezers.

Slide of treating ear of screwworm infested pig. Photo by USDA Animal and Plant Health Inspection Service

Any open wound is attractive to the New World screwworm, either natural or human-inflicted. Female screwworm eggs reach maturity within five days after hatching. This can result in up to 3,000 larvae being present in a single wound.

“They get into a wound, and even if you have a chemical control, it won’t heal the wound,” Swiger said. For now, she says the most effective prevention method is to watch your animals.

5. Human cases are cringeworthy

Yes, what follows is gross.

A 4-year-old girl in India was once treated for a screwworm infestation inside her rectum. Her rectal ulcer had grown to 1.9 inches by 1.2 inches. That’s roughly twice the size of a quarter.

“[The] wound became maggot free in four days during which hundreds of whitish briskly motile maggots measuring 10-18 mm [0.39 – 0.71 inches long] were retrieved,” according to a case report from Department of Pediatrics at RD Gardi Medical College.

Another case of a 12-year-old girl was reported in 2008, after she returned to the U.S. from a trip in Colombia. Doctors in Connecticut had to manually extract 142 larvae from the girl’s scalp.

6. Salvation is coming by way of Panama

Early eradication programs in the 1950s involved sterilizing male screwworm flies with cobalt-60 gamma ray radiation. Dr. Edward F. Knipling (pictured) and Dr. Raymond C. Bushland pioneered the technique. Photo by USDA Agricultural Research Service

In 1972, the U.S. and Mexico established the Screwworm Eradication Program agreement. By 1991, Animal and Plant Health Inspection Service had a 6-year action plan to eradicate the screwworm from all of Central and North America.

The plan involved using planes to airdrop sterile male flies across hard hit regions.

To achieve maximum eradication, the Mexico-United States Commission developed flight paths to release millions of sterile flies in Mexico, Panama, El Salvador, Costa Rica and other areas at risk including Texas, Arizona and California.

The mutant males competed with normal ones for females, and ultimately wiped out the New World screwworm population from the U.S. and Mexico by 1984.

But eradication labs tend to move south, once an affected area has been eradicated. Today, USDA and its partners maintain a permanent sterile fly barrier between Panama and Colombia to prevent the establishment of any deadly flies from South America. The screwworm rearing facility is located in Pacora, Colombia, and is capable of producing 200 million flies per week.

“We still have screwworms being produced in the eradication program, in Panama, which is shipping worms to Florida,” Swiger said. This transport process started on October 11 for the Florida Keys.

7. If the screwworm outbreak spreads, it’ll cost us

Now that screwworms are back, Swiger expects eradication efforts to take months.

“I don’t know if they’ll ever figure it out how it got there. In the past, we know people traveled with animals. But this is a wild native species and finding several deer infested is troubling especially when it has not been reported how,” Swiger said.

Flies on their own can travel several miles without any wind behind them. Good news is Hurricane Matthew did not directly hit the Keys, which makes additional infestations less likely.

Photograph of Edward F. Knipling with colleagues inspecting ground meat. In the 1950s, ground meat, beef blood and water were used to raise screwworms in the lab. Photo by USDA Agricultural Research Service

The main worry at the moment revolves around a lack of surveillance, Swiger said. Most fly species fall for traps, but such devices don’t exist for screwworms.

That’s too bad because the stakes are high for livestock owners. The cattle market was so affected by the last outbreak that the nation was essentially forced into an eradication program, Swiger said.

By 1930, screwworms had spread to the southeast, where livestock producers in the U.S. were losing $400 million annually. In 1957, Florida state legislature allotted $3 million for an eradication program.

These days, USDA estimates the nation’s livestock industry could lose $750 million a year from a widespread screwworm outbreak.