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 US agricultural industry officials and triggering the closure of several border-area cattle, horse and bison trading ports.

It wouldn’t be the first time the US has had to battle these invasive bugs. The nation 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 — essentially fighting flies with flies — 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.