Sterile Flies vs. the Screwworm, College

Sterile flies beat a flesh-eating fly

The screwworm is a fly whose babies eat living animals. In 2026, the fly is back in Texas for the first time in decades. Years ago, scientists wiped out the fly in the United States by releasing millions of male flies that could not make babies. Now USDA is releasing sterile flies in Texas again.

A bunch of freshly pulled red radishes lying on garden soil — A radish is a root you can eat. Radish comes from the same Latin word *rādīx*.

Your word of the day is

ih-RAD-ih-kayt

e-outfrom Latin ē-

radic-rootfrom Latin rādīx

-atemakes the word an actionfrom Latin -ātus

To get rid of something completely.

Newly laid Mexican fruit fly eggs in a cage of adult flies at a Texas fly-rearing plant

An egg mass is the cluster of eggs a female screwworm lays on a wound. A sterile egg mass never hatches.

Before you read the paper, take a guess. What’s the lowest percent of sterile egg masses that would make screwworm cases in a county start to fall? Give your reason in one sentence.

Hint

Think about how many young flies one fertile egg mass can make.

An aerial view of Sint Michiel Bay on the coast of the island of Curaçao

Read the paper

Baumhover, “A personal account of developing the sterile insect technique to eradicate the screwworm from Curacao, Florida and the southeastern United States,” Florida Entomologist, 2002. The paper is free to read.

Alfred Baumhover, a USDA scientist, worked on the first screwworm eradication programs. His paper tells the story of the 1954 test on the island of Curaçao and the 1957 to 1959 program in Florida. Late in 1958, cases flared up in Broward County, Florida, even while sterile flies were being released there. Table 1 of the paper tracks that outbreak in four-week periods. Notes from the paper. Every period is 4 weeks except the last, which is 2 weeks. Cases are weekly averages and include confirmed and reported cases. Inspectors are the people collecting larvae from wounds. The egg masses for Jan 18 to Feb 14 come only from Jan 18 to 26, 1959. The one egg mass in the last period was fertile, the last sign of wild screwworms in the county.

Period	Cases per week	Egg masses collected	Sterile egg masses	Percent sterile	Sterile males released per square mile per week	Inspectors
Aug 30 to Sep 27, 1958	4.75	no data	no data	no data	400	1.0
Sep 28 to Oct 25, 1958	8.00	no data	no data	no data	1,150	1.0
Oct 26 to Nov 22, 1958	20.50	no data	no data	no data	1,875	1.0
Nov 23 to Dec 20, 1958	22.00	55	41		3,600	5.5
Dec 21, 1958 to Jan 17, 1959	33.00	131	100		4,300	5.2
Jan 18 to Feb 14, 1959	9.75	44	39		10,600	9.2
Feb 15 to Feb 28, 1959	0.50	1	0		10,600	4.0

Florida Cracker cattle beside the St. Cloud Canal in central Florida

From Nov 23 to Dec 20, 1958, inspectors in Broward County collected 55 egg masses, and 41 were sterile.

In Baumhover’s Table 1, ____ of the egg masses collected from Nov 23 to Dec 20, 1958 were sterile.

See the table

Period	Cases per week	Egg masses collected	Sterile egg masses	Percent sterile	Sterile males released per square mile per week	Inspectors
Aug 30 to Sep 27, 1958	4.75	no data	no data	no data	400	1.0
Sep 28 to Oct 25, 1958	8.00	no data	no data	no data	1,150	1.0
Oct 26 to Nov 22, 1958	20.50	no data	no data	no data	1,875	1.0
Nov 23 to Dec 20, 1958	22.00	55	41		3,600	5.5
Dec 21, 1958 to Jan 17, 1959	33.00	131	100		4,300	5.2
Jan 18 to Feb 14, 1959	9.75	44	39		10,600	9.2
Feb 15 to Feb 28, 1959	0.50	1	0		10,600	4.0

A fly-rearing specialist sifts Mexican fruit fly eggs collected from egg-laying panels

From Jan 18 to Feb 14, 1959, inspectors collected 44 egg masses, and 39 were sterile.

In Baumhover’s Table 1, ____ of the egg masses collected from Jan 18 to Feb 14, 1959 were sterile.

See the table

Period	Cases per week	Egg masses collected	Sterile egg masses	Percent sterile	Sterile males released per square mile per week	Inspectors
Aug 30 to Sep 27, 1958	4.75	no data	no data	no data	400	1.0
Sep 28 to Oct 25, 1958	8.00	no data	no data	no data	1,150	1.0
Oct 26 to Nov 22, 1958	20.50	no data	no data	no data	1,875	1.0
Nov 23 to Dec 20, 1958	22.00	55	41		3,600	5.5
Dec 21, 1958 to Jan 17, 1959	33.00	131	100		4,300	5.2
Jan 18 to Feb 14, 1959	9.75	44	39		10,600	9.2
Feb 15 to Feb 28, 1959	0.50	1	0		10,600	4.0

A brown calf standing in a green pasture in Brenham, Texas

In Baumhover’s Table 1, what did Broward County’s cases per week do while about 75% of egg masses were sterile?

See the table

Period	Cases per week	Egg masses collected	Sterile egg masses	Percent sterile	Sterile males released per square mile per week	Inspectors
Aug 30 to Sep 27, 1958	4.75	no data	no data	no data	400	1.0
Sep 28 to Oct 25, 1958	8.00	no data	no data	no data	1,150	1.0
Oct 26 to Nov 22, 1958	20.50	no data	no data	no data	1,875	1.0
Nov 23 to Dec 20, 1958	22.00	55	41		3,600	5.5
Dec 21, 1958 to Jan 17, 1959	33.00	131	100		4,300	5.2
Jan 18 to Feb 14, 1959	9.75	44	39		10,600	9.2
Feb 15 to Feb 28, 1959	0.50	1	0		10,600	4.0

A technician inside a plane starts the machine that sends sterile screwworm flies out a chute over Texas

In Baumhover’s Table 1, the last release rate of 10,600 sterile males per square mile per week was ____ times the first rate of 400.

See the table

Period	Cases per week	Egg masses collected	Sterile egg masses	Percent sterile	Sterile males released per square mile per week	Inspectors
Aug 30 to Sep 27, 1958	4.75	no data	no data	no data	400	1.0
Sep 28 to Oct 25, 1958	8.00	no data	no data	no data	1,150	1.0
Oct 26 to Nov 22, 1958	20.50	no data	no data	no data	1,875	1.0
Nov 23 to Dec 20, 1958	22.00	55	41		3,600	5.5
Dec 21, 1958 to Jan 17, 1959	33.00	131	100		4,300	5.2
Jan 18 to Feb 14, 1959	9.75	44	39		10,600	9.2
Feb 15 to Feb 28, 1959	0.50	1	0		10,600	4.0

A larval room filled with trays of Mexican fruit fly larvae at a Texas fly-rearing plant

From Nov 23, 1958 to Jan 17, 1959, about 3 of every 4 egg masses in Broward County were sterile, yet cases rose.

If 1 screwworm egg mass in 4 is fertile, each fertile egg mass must make more than ____ breeding females for the population to grow.

See the table

Period	Cases per week	Egg masses collected	Sterile egg masses	Percent sterile	Sterile males released per square mile per week	Inspectors
Aug 30 to Sep 27, 1958	4.75	no data	no data	no data	400	1.0
Sep 28 to Oct 25, 1958	8.00	no data	no data	no data	1,150	1.0
Oct 26 to Nov 22, 1958	20.50	no data	no data	no data	1,875	1.0
Nov 23 to Dec 20, 1958	22.00	55	41		3,600	5.5
Dec 21, 1958 to Jan 17, 1959	33.00	131	100		4,300	5.2
Jan 18 to Feb 14, 1959	9.75	44	39		10,600	9.2
Feb 15 to Feb 28, 1959	0.50	1	0		10,600	4.0

Which conditions in Broward County helped young screwworms survive during the 1958 to 1959 outbreak?

See the table

Period	Cases per week	Egg masses collected	Sterile egg masses	Percent sterile	Sterile males released per square mile per week	Inspectors
Aug 30 to Sep 27, 1958	4.75	no data	no data	no data	400	1.0
Sep 28 to Oct 25, 1958	8.00	no data	no data	no data	1,150	1.0
Oct 26 to Nov 22, 1958	20.50	no data	no data	no data	1,875	1.0
Nov 23 to Dec 20, 1958	22.00	55	41		3,600	5.5
Dec 21, 1958 to Jan 17, 1959	33.00	131	100		4,300	5.2
Jan 18 to Feb 14, 1959	9.75	44	39		10,600	9.2
Feb 15 to Feb 28, 1959	0.50	1	0		10,600	4.0

Sterile Mexican fruit flies being packed into boxes for release from planes at a Texas fly-rearing plant

Around Jan 26, 1959, sterile females released from the rearing plant began laying sterile eggs in Broward County.

Why would counting Broward County egg masses laid after Jan 26, 1959 make sterile matings among wild screwworms look more common than they were?

See the table

Period	Cases per week	Egg masses collected	Sterile egg masses	Percent sterile	Sterile males released per square mile per week	Inspectors
Aug 30 to Sep 27, 1958	4.75	no data	no data	no data	400	1.0
Sep 28 to Oct 25, 1958	8.00	no data	no data	no data	1,150	1.0
Oct 26 to Nov 22, 1958	20.50	no data	no data	no data	1,875	1.0
Nov 23 to Dec 20, 1958	22.00	55	41		3,600	5.5
Dec 21, 1958 to Jan 17, 1959	33.00	131	100		4,300	5.2
Jan 18 to Feb 14, 1959	9.75	44	39		10,600	9.2
Feb 15 to Feb 28, 1959	0.50	1	0		10,600	4.0

USDA animal health staff inspect cattle at the border crossing in Douglas, Arizona

In Broward County, more than 36% of screwworm wounds held mature larvae ready to pupate, and some ranchers stopped treating infested calves.

Why does the sterile insect technique depend on ranchers inspecting and treating screwworm wounds?

See the table

Period	Cases per week	Egg masses collected	Sterile egg masses	Percent sterile	Sterile males released per square mile per week	Inspectors
Aug 30 to Sep 27, 1958	4.75	no data	no data	no data	400	1.0
Sep 28 to Oct 25, 1958	8.00	no data	no data	no data	1,150	1.0
Oct 26 to Nov 22, 1958	20.50	no data	no data	no data	1,875	1.0
Nov 23 to Dec 20, 1958	22.00	55	41		3,600	5.5
Dec 21, 1958 to Jan 17, 1959	33.00	131	100		4,300	5.2
Jan 18 to Feb 14, 1959	9.75	44	39		10,600	9.2
Feb 15 to Feb 28, 1959	0.50	1	0		10,600	4.0

A narrow window inside a plane shows sterile screwworm flies entering the release chute, with Texas land passing below

Table 1 of Baumhover’s 2002 paper follows one Florida county through one screwworm outbreak.

Which summary fits Table 1 of Baumhover’s 2002 paper?

USDA workers give medicine to a deer and mark it on Big Pine Key, Florida, during a screwworm outbreak

Which question can’t Table 1 of Baumhover’s paper answer?

A sterile screwworm fly on the window of a plane flying over Texas near the Mexico border

Lesson complete

Today’s word

eradicate

ih-RAD-ih-kayt

To remove or destroy utterly.

Back to the lesson Start over

Up nextinsulinThe Lizard Behind Ozempic

Sources

Edward F. Knipling, USDA, Golden Goose Award profile, 2016
Roy Melvin and Raymond C. Bushland, USDA, 1936 and 1940, as described in Baumhover, 2002
USDA Animal and Plant Health Inspection Service, with the Texas Animal Health Commission, USDA, June 3, 2026 and June 5, 2026
COPEG, run jointly by USDA and Panama’s Ministry of Agriculture Development, USDA sterile fly production page
R. Henry, Emerging Infectious Diseases, 2019
USDA National Agricultural Library, “STOP Screwworms” exhibit
USDA APHIS, Animal Health Officials Respond to Second Detection of New World Screwworm in the United States, June 5, 2026
USDA APHIS, New World screwworm, Using sterile insect technique, Sterile fly production and dispersal, Screwworm.gov and Current status
Vision and Change core concepts and competencies, as summarized in Brownell and others, CBE Life Sciences Education, 2014
Word origins from Dictionary.com: eradicate, radical, radish, radicle, voracious, carnivore, Homo sapiens
Spanish and French words from Wiktionary: eradicate, radix

Sterile Flies vs. the Screwworm, College

Sterile flies beat a flesh-eating fly

Your word of the day is

Before you read the paper, take a guess. What’s the lowest percent of sterile egg masses that would make screwworm cases in a county start to fall? Give your reason in one sentence.

Read the paper

In Baumhover’s Table 1, ____ of the egg masses collected from Nov 23 to Dec 20, 1958 were sterile.

In Baumhover’s Table 1, ____ of the egg masses collected from Jan 18 to Feb 14, 1959 were sterile.

In Baumhover’s Table 1, what did Broward County’s cases per week do while about 75% of egg masses were sterile?

In Baumhover’s Table 1, the last release rate of 10,600 sterile males per square mile per week was ____ times the first rate of 400.

If 1 screwworm egg mass in 4 is fertile, each fertile egg mass must make more than ____ breeding females for the population to grow.

Which conditions in Broward County helped young screwworms survive during the 1958 to 1959 outbreak?

Why would counting Broward County egg masses laid after Jan 26, 1959 make sterile matings among wild screwworms look more common than they were?

Why does the sterile insect technique depend on ranchers inspecting and treating screwworm wounds?

Which summary fits Table 1 of Baumhover’s 2002 paper?

Which question can’t Table 1 of Baumhover’s paper answer?

Lesson complete

Today’s word

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