BOZEMAN - Montana's Department of Livestock issued a new animal health order on June 4, requiring import permits and veterinary inspections for animals entering the state from infested areas.
The New World screwworm, a destructive parasitic fly, has been detected in the United States for the first time since 1966. The fly was first found in Zavala County, Texas, on June 3, with five additional cases now confirmed in South Texas.
Scientists with Montana State University Extension have raised concerns about the pest, and the Montana Department of Livestock has responded with a new animal health order issued June 4.
The order affects all warm-blooded animals traveling into Montana from infested areas, including cattle, horses, dogs, cats, sheep, pigs, birds, and rabbits.
Animals from affected states must have an import permit, a Certificate of Veterinary Inspection confirming the animal is free from wounds and shows no signs of screwworm larvae, and official identification.
The certificate must be issued within five days before the animal moves to Montana and cannot be issued before the initial detection in the infected state.
Because Texas authorities do not have jurisdiction over small animals, the Montana order applies different rules by species. Rules for small animals apply statewide, while rules for livestock apply at the county level.
The New World screwworm poses a serious threat to living animals. The flies lay eggs in the wounds of living animals, and the larvae feed on living tissue, causing severe damage. The larvae eventually drop to the ground and hatch into adult flies.
Officials are working to stop the spread by releasing sterile male flies into the population. Because female flies only reproduce once in their lifetime, this method helps reduce the number of new flies.
Anyone bringing animals into Montana from areas near the infested zones should monitor them closely for any signs of screwworm infection.
The Montana Department of Livestock can be contacted at 406-444-2976 or mtstatevet@mt.gov for more information regarding animal travel within and around the infected zones.
Additional tools and information related to the response to New World screwworm can also be found on the USDA Animal and Plant Health Inspection Service website at https://www.aphis.usda.gov/animal-emergencies/nws [aphis.usda.gov].
To learn more about the Montana Department of Livestock animal health order, visit https://news.mt.gov/Department-of-Livestock/Animal-Health-Order-No-2026-01 [news.mt.gov].
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