Level 1 - Absolute Beginner

There is a dangerous fly called the screwworm. Its baby worms eat the living skin of animals. This fly was removed from the United States many years ago. Now it has come back.

Scientists found the screwworm in a baby cow in Texas on June 3, 2026. The last time this fly was found in Texas was in 1966. That is 60 years ago.

To stop the fly from spreading, scientists are releasing special flies that cannot have babies. They are also keeping all animals inside a 12-mile area. They want to protect cows and other animals from this dangerous parasite.

parasite

a living thing that lives on or inside another living thing and harms it

larvae

the young form of an insect before it grows into an adult

eradicated

completely removed or destroyed so it no longer exists in a region

quarantine zone

an area where animals or people are kept separate to stop the spread of a pest or disease

sterile

not able to reproduce or have young

detection

the discovery of something, especially something small or dangerous

cattle

cows and bulls kept on a farm for meat or milk

livestock

animals kept on a farm, such as cows, pigs, sheep, and chickens

Level 2 - Elementary

The US Department of Agriculture confirmed on June 3, 2026 that a deadly parasite known as the New World screwworm had been found in a three-week-old calf in Zavala County, South Texas. The screwworm fly lays its eggs in open wounds on warm-blooded animals. When the eggs hatch, the larvae feed on living tissue, which can kill the animal if not treated quickly.

The case marks the first confirmed detection in the continental United States since the parasite was fully eradicated in 1966. A program using sterile flies -- flies that have been treated so they cannot reproduce -- successfully eliminated the pest from the country decades ago. However, the fly has remained present in parts of Central America and the Caribbean.

Officials responded quickly by establishing a 12-mile quarantine zone around the affected farm and releasing large numbers of sterile flies into the area. The movement of warm-blooded animals including cattle, horses, and pets is now restricted in the zone. Agriculture Secretary Brooke Rollins called it the highest-priority threat to the US cattle industry.

New World screwworm

a parasitic fly whose larvae feed on the living tissue of warm-blooded animals, native to the Americas

tissue

the material that makes up a living creature's body, such as muscle or skin

eradication

the complete elimination of a pest, disease, or species from a region

sterile fly program

a pest-control method that releases flies unable to reproduce to reduce a wild population

open wound

a break in the skin or body surface where parasites or infection can enter

quarantine

the separation of animals or people to prevent the spread of disease or pests

agriculture secretary

the head of the government department responsible for farming and food production

infestation

the presence of large numbers of harmful insects or pests in a particular area

Level 3 - Intermediate

Federal agriculture officials confirmed on June 3, 2026 that a case of New World screwworm, a parasitic fly once considered among the most economically damaging livestock pests in North America, had been identified in a calf in Zavala County, South Texas. The confirmation marks the first detection in the continental United States since a coordinated eradication campaign using the Sterile Insect Technique eliminated the species from the country in 1966.

The New World screwworm, Cochliomyia hominivorax, is a fly whose females deposit eggs directly into wounds or mucosal openings of warm-blooded hosts. The resulting larvae feed on living tissue, creating a self-enlarging wound that can be fatal within days if untreated. Though the parasite rarely infects humans, its economic impact on cattle, deer, and other livestock can be severe and widespread.

The USDA responded by establishing a 12-mile quarantine zone around the affected property in La Pryor, restricting the movement of warm-blooded animals, and deploying aerial releases of sterile flies to disrupt the pest's reproductive cycle. Texas A&M AgriLife Extension was activated alongside federal inspectors to monitor farms within the zone. Agriculture Secretary Brooke Rollins described the discovery as requiring 'all available tools' to prevent a resurgence.

Sterile Insect Technique (SIT)

a pest-control method in which large numbers of sterilized insects are released to mate unsuccessfully with wild populations, reducing the population over time

mucosal opening

a moist body opening, such as the nose or navel, where a parasitic fly may deposit its eggs

self-enlarging wound

a wound that grows larger as larvae feed on surrounding tissue, making treatment increasingly difficult

aerial release

the dispersal of sterile insects from aircraft over a targeted geographic area

reproductive cycle

the series of biological events by which an organism produces offspring

resurgence

the return of a pest or disease after it had been controlled or eliminated

biosecurity

measures taken to prevent the introduction or spread of harmful organisms, diseases, or pests

economic threshold

the point at which the damage caused by a pest exceeds the cost of controlling it

Level 4 - Advanced

The June 3, 2026 confirmation by USDA-APHIS of a New World screwworm, Cochliomyia hominivorax, in a three-week-old calf in Zavala County, Texas, represents the most significant breach in US agricultural biosecurity since the parasite was declared eradicated from the continental United States in 1966 following a joint US-Mexico Sterile Insect Technique campaign that had been underway since 1958. The case was identified by a state veterinarian following a standard wound inspection; laboratory confirmation required PCR-based species identification to distinguish C. hominivorax from its non-parasitic congener C. macellaria.

The life history of C. hominivorax makes it uniquely damaging: gravid females are obligate parasites of living tissue, ovipositing in wounds as small as two millimeters, tick bites, or mucosal membranes of neonate animals. Eclosion and tissue invasion occur within 12 to 21 hours; larval masses of up to 200 individuals can consume three to four square centimeters of host tissue per day, producing a self-excavating lesion that becomes lethal within four to seven days in untreated animals. US cattle herds, representing an industry valued at approximately $300 billion, have had no significant screwworm exposure for sixty years and carry essentially zero herd immunity.

The USDA's immediate response -- a 12-mile quarantine radius around the La Pryor focus, aerial sterile-fly releases from USDA's Panama-based production facility supplemented by an emergency expansion of the Presidio, Texas rearing plant -- mirrors the methodology that achieved eradication in the 1960s. The key epidemiological question is whether the Zavala County case represents an isolated incursion from the endemic zone maintained in the Darien Gap and northern Colombia, or the leading edge of a range expansion facilitated by reduced sterile-fly buffer zones along the US-Mexico border.

USDA-APHIS

the US Department of Agriculture's Animal and Plant Health Inspection Service, the federal agency responsible for protecting agricultural resources from pests and disease

PCR (polymerase chain reaction)

a laboratory technique that amplifies specific DNA sequences for precise species-level identification of organisms

obligate parasite

an organism that can only complete its life cycle by living on or in a specific type of host

ovipositing

the act of depositing eggs by a female insect into a specific site favorable to larval development

eclosion

the hatching of larvae from insect eggs, marking the beginning of the larval feeding stage

self-excavating lesion

a wound that grows progressively larger as feeding larvae remove tissue layer by layer

herd immunity

a level of resistance in a population to a disease or parasite that limits its spread, typically built through prior exposure or vaccination