Screwworm flies attack pets in the US: four dogs and a cat hit this week

The New World screwworm (NWS), a parasitic fly whose larvae feed on the living flesh of animals, has spread to a third US state, Arizona, according to Ars Technica. The insect was previously found in New Mexico and Texas. This week, attacks were recorded on four dogs and a cat.

The scale so far

Since the flies re-invaded the United States in June, 74 animal cases have been identified. The flies lay hundreds of eggs in wounds and moist body openings. The hatched larvae resemble screws, bore into living tissue and cause severe, sometimes fatal wounds. They then drop to the ground and develop into adult flies.

How the flies were once beaten back

Because of the damage they do to livestock, the flies were eliminated from the US in the 1960s by releasing sterile male flies from aircraft, which prevents successful breeding. For years afterward, a biological barrier in the Darién Gap, on the border between Panama and Colombia, kept them at bay. That barrier was breached in 2022, and the flies made their way back to the US through Central America.

Not only a livestock problem

The parasites are mostly regarded as a threat to the livestock industry, but they can also devastate wildlife and domestic pets and, more rarely, harm people. Mexico's Ministry of Health reports 806 confirmed human infestations since the flies reemerged, and nine people have died.