Savannah, GA |

For many producers today, the New World screwworm is something they’ve only read about in textbooks. But according to University of Georgia Extension veterinary entomologist Nancy Hinkle, the threat it poses to livestock and wildlife is very real — and many in agriculture may not be prepared if it reappears.

Unlike most flies that simply irritate animals, screwworms are far more dangerous because of how they reproduce.

“They infest living tissue — only living tissue,” Hinkle said. “You’re not going to find these maggots in a dead dog on the side of the road. You’re going to find them in your calf over in the calf hutches. And if they’re already in the navel area and eating away at the calf, unless you get in there and do something quickly, that calf is going to die. Without human intervention, an animal that is infested with screwworms will die.”

A Threat Beyond Livestock

While cattle producers would certainly feel the impact, the potential danger goes far beyond just livestock. Screwworms can infest a wide variety of animals, including wildlife — which could allow populations to spread rapidly.

“Now, we’re not just talking cattle, pigs, or sheep,” Hinkle explained. “We’re talking raccoons, possums, rats, and whitetail deer. Think about it — Georgia has over two million whitetail deer. Each one of those is potentially a nursery for screwworms.”

That widespread host range could make controlling the pest particularly challenging if it were to reappear in the United States.

“Think about the possibility for screwworm populations rebounding and exploding because of the wildlife and other life that we have here,” Hinkle said. “And let me mention also that screwworms do not differentiate — they will attack humans as well.”

Very Different from Typical Fly Problems

One of the challenges with screwworms is that they behave very differently than the flies producers typically deal with around their farms.

“Screwworms are completely different from any of the other flies we’ve had to deal with — face flies, stable flies, horn flies, other flies around the dairy,” Hinkle said. “With most flies, it’s the adult that’s the problem. But now we’re having to look at the immature stage — the larvae, the maggots — as the problem.”

That difference requires a completely different approach to management.

“We don’t care about those adult flies flying around,” she said. “They’re not a problem except that they’re going to produce the next generation. What we want to treat are the maggots, because they’re the ones that are eating living flesh.”

Preparation and Awareness Are Key

Currently, there is little producers can do to actively prevent screwworms from appearing in the United States. However, Hinkle says awareness and preparation are critical if the pest were to return.

“The good news is there’s really nothing we can do to prevent screwworms from coming in,” she said. “But the good news is also that we can’t do anything yet. So right now, we need to be informed and think about what we would do if it shows up.”

One of the most important steps producers can take now is building a strong relationship with their veterinarian, as most treatments require professional guidance.

“The one thing we can do is establish a good relationship with our veterinarian,” Hinkle said. “Most of the treatments that are coming along for screwworms are prescription only. So you need to have a plan in place if this situation arises.”

While the New World screwworm hasn’t returned to the United States, experts say staying informed could make the difference between a manageable situation and a devastating outbreak for livestock producers.

By: John Holcomb