New World Screwworm

Ready Reference Guide—Historical Economic Impact

December 2016 USDA APHIS Veterinary Services • National Preparedness and Incident Coordination (NPIC) 1 of 2

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Historical Economic Impact Estimates of New World Screwworm (NWS) in the United States

1930–1940s 

Though NWS was present in the southwestern United States (map below) since at least 1842, the pest was first documented

as a significant problem in the Southeast in 1933, following shipments of infested animals from the Southwest. Inundated by 

calls for help from producers in the rapidly-expanding NWS affected areas, USDA and the southeastern States engaged in the 

Screwworm Educational Program in 1935 to instruct producers on how to prevent livestock infestations. The Federal 

government and the State of Florida committed $978,463* to this program over nearly three years, in addition to 

undocumented contributions from other States. In 1941, the USDA announced the success of a $60,000* program to develop 

a targeted NWS insecticide (Smear 62) to mitigate producer losses, which were valued at $5–10 million* per year nationwide

during this period. During these decades, USDA scientists had developed a method to raise large numbers of NWS larvae and 

began to look for a method to sterilize flies so they could not reproduce. [*Indicates figure is not adjusted for inflation]

1950–1960s

Radiation was discovered as an effective method to sterilize NWS flies; in the fall of 1951, the first test site was established in 

Florida. Experiments continued in the early 1950s, demonstrating success of the Sterile Insect Technique (SIT). Producers in 

the southeastern United States experienced losses up to $10–20 million* per year prior to NWS eradication in 1959. This

eradication was the result of over a year of SIT and an investment of $10 million* from the Federal government and the State 

of Florida. At this time, producers in the southwestern United States lost between $50–100 million* annually due to NWS. 

Presumably, these increased losses in the Southwest were due to higher livestock populations, larger geographic area, and/or

greater potential for NWS to overwinter. The success of the eradication program in the Southeast led to the initiation of an 

eradication program for the Southwest in 1962. Funded by the Federal government, States in the Southwest Eradication Area 

(Texas, New Mexico, Arkansas, Louisiana, and Oklahoma), and the rancher-led nonprofit, Southwest Animal Health Research 

Foundation, this eradication program was declared a success in 1966. It ultimately cost $32 million* to complete, establishing

a NWS barrier zone along the U.S./Mexico border. 

1970s

By the mid-1970s, the estimated economic

benefit of NWS eradication programs to U.S. 

producers was $200 million* per year.

However, the continued presence of NWS in

Mexico resulted in recurrent outbreaks in the 

Southwest. An analysis of NWS economic 

impacts in Texas in 1976 indicated that 

livestock producers spent $132.1 million* per 

year to manage NWS outbreaks, with a total

impact to the Texan economy of $283–375 

million*. The difficulty of maintaining the 

barrier zone along the U.S./Mexico border 

and the impact of these outbreaks led to 

the creation of the joint Mexico-U.S.

Screwworm Eradication Commission to drive 

NWS to Mexico’s southern borders, which

was achieved in 1986.

Economic Benefits of U.S. Eradication

The eradication of NWS in the United States 

yielded annual economic benefits to producers 

estimated at $796 million* in 1996, with an estimated 

$2.8 billion* benefit to the wider economy.
New World Screwworm

Ready Reference Guide—Historical Economic Impact

December 2016 USDA APHIS Veterinary Services • National Preparedness and Incident Coordination (NPIC) 2 of 2

4700 River Road Unit 41 • Riverdale, MD 20737

Costs Associated with NWS Infestations

Before eradication, producers experienced significant 

losses due to NWS, including costs from the following:

 Animal deaths

 Decreased livestock production

 Decreased availability of draught animals and 

manure

 Increased need for veterinary services

 Increased need for medication and insecticide

 Extra labor and vehicle costs for the inspection and 

treatment of infested animals.

Costs of response activities, paid for by States, the Federal 

government, and nonprofits, included

 public education,

 research for more effective treatments,

 surveillance activities, and

 SIT expenditures.

Example Breakdown of Producer Costs

An analysis of producer costs due to an NWS outbreak in Texas 

in 1976 indicated that producers spent $132.1 million (not 

adjusted for inflation) that year in response to the pest, with 

the total cost broken down into the following categories:

Potential Economic Impact of NWS in 2016

Despite the maintenance of a barrier zone barrier zone along 

the U.S./Mexico border after the eradication of NWS in the 

U.S. in 1966, southwestern States experienced recurrent

Mexican-origin NWS outbreaks. Along with vigilant 

surveillance and prompt isolation and treatment of infested 

animals, outbreaks were managed using SIT until the barrier 

zone moved south of the U.S./Mexico border. An economic 

analysis1 of the 1976 NWS outbreak in Texas indicated that 

1,488,256 cattle and 332,600 sheep and goats were infested 

with NWS that year. Assuming equivalent livestock populations

and NWS infection rates as in the case study in 1976 Texas, the 

total cost per NWS case was adjusted for inflation to 2016 

dollars. The table to the right shows the livestock populations, 

NWS infestation rates, and costs included in this calculation.

NWS Losses: 

Texas Data 1976 Results 2016 Results 

(adjusted for inflation only)

Cattle Population 7,224,515 -

Cattle Infestation Rate 20.60% -

Cattle Cost/Case $81.51 $346.28 

Sheep & Goat Population 3,654,945 -

Sheep & Goat Infest. Rate 9.10% -

Sheep & Goat Cost/Case $32.38 $137.56 

Total Cattle Cost $121,307,258 $515,351,210 

Total Sheep & Goat Cost $10,769,588 $45,752,456 

Texas Producers Losses $132,076,846 $561,103,666 

Texas Economy Loss $329,598,005 $1,400,235,237 

The results of adjusting for inflation indicate that a NWS outbreak of 

the roughly moderate magnitude of the 1976 outbreak could cost 

Texas producers $561 million per year and the Texas economy a loss 

of $1.4 billion. Numerous factors make this comparison, over forty 

years after NWS eradication, difficult. The cattle population of Texas 

in 2016 is significantly larger (11 million) while the sheep and goat 

population is lower (1.6 million). There are a multitude of other 

factors that could affect the economic impact of NWS in 2016 and 

require further quantification, including husbandry and veterinary 

practices, economic output multipliers, costs of response activities, 

and potential NWS infection rates. The results presented here 

demonstrate the potential of NWS infestations in the United States 

to have a significant economic impact.

 

1

Thomas, J.G. (1978). 1977 Screwworm Program in Texas: “Mission 77 - Stamp Out Screwworms.” USDA National Agricultural Library 

Special Collections. Retrieved from https://www.nal.usda.gov/exhibits/speccoll/items/show/7228.