Traveling With Pets: 411 on New World Screwworms

Protect your pets from this new threat.

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Part of the Florida Keys have been under an agricultural state of emergency since early October following the reappearance of a flesh-eating maggot not seen in the state in 50 years. Despite the dreadful connotations, so far the screwworms have only affected deer and a small number of pets. With snowbird season around the corner, here's everything you need to know to keep your pets safe and enjoy some stress-free downtime.

If you're into insects, this guy may be for you. Why its called a Secondary Screwworm Fly is because the original screwworm fly was eradicated. Nonetheless, this blowfly makes an interesting conversation piece.


The adult New World screwworm fly.

Photo by: Bob Balestri

Bob Balestri

It’s been a rough year for Florida: Miami is battling the Zika virus, Hurricane Matthew pummeled the state’s Atlantic coast, and now the Florida Keys are racing to eradicate the New World screwworm, the flesh-eating maggot offspring of the New World screwworm fly.

On October 3, 2016, Florida Commissioner of Agriculture Adam H. Putnam declared an agricultural state of emergency for Monroe Country after the U.S. Department of Agriculture (USDA) confirmed the resurgence of screwworms on Big Pine Key. It’s the first time in more than 50 years that screwworms have surfaced in Florida, and more than 30 years since they were eliminated from the U.S. The cause behind the current outbreak is unknown, and Commissioner Putnam could not be reached for an update. Screwworms target warm-blooded animals, and pose a potential threat to the state’s livestock industry, which earns more than $2.78 billion a year.

The zombie-like maggots infect their host after a female screwworm fly lays her eggs in, or near, an open wound, and the hatched larvae then feast upon the host's flesh. If left untreated, screwworms can kill in as little as a week. So far the endangered Key deer, which numbered about 1,000 at the start of the infestation, have been the most impacted. As of October 27, the U.S. Fish and Wildlife Service confirmed that 115 deer have been euthanized due to screwworm infections that were too far advanced to treat. Key deer are a variation of the white-tailed deer, and are only found in the lower Florida Keys.

As of October 28, USDA lab tests have also confirmed positive local cases in one dog, two cats and a pig. All of the animals resided outdoors on Big Pine Key and No Name Key.

However, at this point there’s no reason for visitors and seasonal residents to avoid coming or to leave their pets behind as long as preventative measures are taken. Florida State Veterinarian Dr. Michael Short advises checking animals at least once a day for any open wounds. Wounds with abnormal discharge or drainage and a bad odor are early warning signs, along with low energy and loss of appetite. Maggots may also be visible in the wound within the first day or two, but the good news is that screwworms are fully treatable with early detection.

Dr. Doug Mader of Marathon Veterinary Hospital, the largest in the Keys, says the practice hasn’t seen any new cases beyond those that have been confirmed by the USDA. Dr. Mader happens to live on Big Pine Key, where some of the confirmed cases originated, and owns two dogs that live outside. “This is a concerning situation, but people shouldn’t be afraid,” he says. “We can save being afraid for Halloween.” That said, he recommends checking outdoor pets twice a day, since screwworms mature from egg to maggot in 21 hours. If your pet does have a wound, Dr. Mader advises covering the wound and keeping the pet inside until it heals. Otherwise, “If a pet is outside and has no wounds, it will not be affected by screwworms,” he says.

To help prevent screwworms from spreading beyond the Keys, the Florida Department of Agriculture and Consumer Services (FDACS) has taken the additional step of setting up a quarantine zone for all animals entering and leaving the area, including pet dogs, cats, birds, rabbits, etc. The Animal Health Check Zone stretches from Mile Marker 91 in Key Largo to Mile Marker 0 in Key West. A checkpoint station has been established in Key Largo at Mile Marker 106 for those traveling north, and involves a brief inspection. So far more than 2,000 animals have been screened and tested negative, including dogs, cats, horses, chickens and birds. Animals that are suspected to have screwworms will either be examined by an on-site veterinarian or referred to a local veterinarian for treatment.

In addition, contact your local veterinarian if you suspect your pet has screwworms, or call 1-800-435-7352 for help. Non-Florida residents should call 850-410-3800. Additionally, travelers and locals alike can visit to upload photos of suspected cases for FDACS veterinarians. Report suspected cases in deer by calling 1-888-404-3922.

Even though screwworms can spread to people, instances are rare, and so far no cases have been reported. Early symptoms usually involve itching and discomfort at the wound site; seek immediate medical attention for any suspected cases.

While efforts to contain screwworms are underway, FDACS announced on October 18 that they had spread to six neighboring areas: Big Torch Key, Middle Torch Key, Little Torch Key, Cudjoe Key, Ramrod Key and Summerland Key. In response, the federal and state levels have rapidly deployed the Sterile Insect Technique (SIT), which involves releasing sterile male screwworm flies into the affected regions in order to prevent further reproduction. This technique has successfully eliminated screwworms in the past.

The agricultural state of emergency is in effect until December 26. Visit for regular updates.

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