Hundreds of millions of flies dropping from planes in the sky might sound like a horrible nightmare, but experts say such a swarm could be the livestock industry’s best defense against a flesh-eating threat poised to invade the southwestern border of the United States.

An outbreak of New World screwworms — the larval form of a type of fly that’s known to nest in the wounds of warm-blooded animals and slowly eat them alive — has been spreading across Central America since early 2023, with infestations recorded in Panama, Costa Rica, Nicaragua, Honduras, Guatemala, Belize and El Salvador. Most Central American countries hadn’t seen an outbreak in 20 years.

The fly reached southern Mexico in November, sparking concern among U.S. agricultural industry officials and triggering the closure of several border-area cattle, horse and bison trading ports.

The U.S. mostly eradicated the New World screwworm populations in the 1960s and 1970s by breeding sterilized males of the species and dispersing them from planes to mate with wild, female flies.

The strategy slowly degraded the insects’ populations by preventing them from laying more eggs. Now, as the insects continue to spread north, officials are hoping the approach could work again.

However, today only one facility in Panama breeds sterilized New World screwworms for dispersal, and hundreds of millions more sterile flies are needed to slow the outbreak.

The U.S. Department of Agriculture has announced plans to open a new “fly factory” in a yet to be determined town near the Texas-Mexico border.

New World screwworms are the parasitic larva of a metallic blue blow fly species called Cochliomyia hominivorax. It feeds on the flesh of living animals, rather than dead ones, said Dr. Phillip Kaufman, a professor at Texas A&M University.

The flesh-eating maggots go for most warm-blooded animals, including horses and cows. They have also been known to infect domestic pets and even humans in rare cases, Kaufman said.

“After mating, the female fly finds a living host, lands on its wound, and will lay up to 200 to 300 eggs,” Kaufman explained. “After 12 to 24 hours, those eggs all hatch, and they immediately start burrowing and feeding on the tissue of that animal, causing very large wounds to form.”

After the larvae feed on the tissue with their sharp mouth hooks for several days, they drop from the animal and burrow into the ground to emerge later as fully grown adult flies.

In a sterile fly production facility, the pupae are subjected to high-energy gamma rays that break down the DNA of the males, damaging their sex chromosomes. The result: impotent adult flies that cause female mates to lay unfertilized eggs. The amount of radiation the male flies are exposed to does not pose a danger to animals or humans. But since the female flies only mate once in their 20-day lifespan, once populations are exposed to sterile males, the populations die out over the course of months or years, depending on the size of the outbreak.(SD-Agencies)

数以亿计的苍蝇从飞机上倾泻而下，听起来像一场可怕的噩梦，但专家表示，这支“昆虫军团”或将成为美国畜牧行业抵御螺旋蝇入侵西南边境的最强防线。自2023年初以来，新大陆螺旋蝇疫情（这种蝇类的幼虫会在温血动物的伤口寄生并蚕食活体）已席卷中美洲。巴拿马、哥斯达黎加、尼加拉瓜、洪都拉斯、危地马拉、伯利兹和萨尔瓦多均报告感染案例——其中多数国家已20年未爆发此类疫情。

2023年11月，螺旋蝇入侵墨西哥南部，引发美国农业官员高度警觉，随即关闭多个边境地区的牛马交易口岸。美国曾在20世纪60-70年代通过培育绝育雄蝇、用飞机空投与野生雌蝇交配的方式，基本根除了新大陆螺旋蝇。这种策略通过阻断繁殖渠道逐步消灭种群。如今随着虫害北扩，当局希望故技重施。

但当前全球仅剩巴拿马一家绝育螺旋蝇培育基地，要遏制疫情还需增产数亿只绝育蝇。美国农业部宣布将在美墨边境城镇新建“苍蝇工厂”，选址待定。得州农工大学教授菲利普•考夫曼博士解释，新大陆螺旋蝇幼虫专食活体动物组织。这些食肉蛆虫主要攻击马牛等温血动物，偶见感染宠物甚至人类案例。

考夫曼说：“雌蝇交配后会寻找活体宿主，在伤口产下200-300枚卵。12-24小时后孵化，幼虫立即钻入动物组织啃食，形成巨大创面。”幼虫用锐利口钩蚕食宿主数日后钻入土中化蛹，最终羽化为成虫。在绝育蝇培育工厂中，蛹接受γ射线照射致使雄蝇DNA断裂、性染色体受损，丧失生育能力。这种辐射量对动植物无害，由于雌蝇20天寿命中只交配一次，只要持续投放绝育雄蝇，种群将在数月到数年内灭绝——具体时长取决于疫情规模。 (Translated by DeepSeek)