screwworm
noun
screw·worm
ˈskrü-ˌwərm 
1
: a blowfly (Cochliomyia hominivorax) of the warmer parts of America whose larva develops in sores or wounds or in the nostrils of mammals including humans with serious or sometimes fatal results
especially
: its larva
2
: any of several flies other than the screwworm and especially their larvae which parasitize the flesh of mammals
Examples of screwworm in a Sentence
Recent Examples on the Web
Despite cattle in this region going to domestic consumption rather than to the U.S., the presence of the screwworm in Mexico has frozen cattle exports to the U.S. nationwide.
—
Isabel Mateos, Fortune, 25 July 2025
Here’s what to know about screwworms and how Texas plans to eradicate the pests.
—Brayden Garcia, Fort Worth Star-Telegram, 23 July 2025
The screwworm first became a significant problem in the United States in 1933, according to the USDA.
—Elizabeth Weise, USA Today, 10 July 2025
After a devastating 1972 outbreak in six states — California, Arizona, New Mexico, Texas, Oklahoma and Arkansas — the United States worked with Mexico to largely eradicate the screwworm.
—Bay Area News Group, Mercury News, 11 July 2025
So far the screwworms have only been seen in Mexico.
—Elizabeth Weise, USA Today, 10 July 2025
But the process of defeating the screwworm may not be quick — or inexpensive.
—Kameryn Griesser, CNN Money, 9 July 2025
With the resurgence of the screwworm, several types of animals are banned from import into the U.S. from Mexico, including:
live cattle
horses
bison
Screwworms life cycle
Where are screwworms located?
—Joyce Orlando, Nashville Tennessean, 13 May 2025
Because the screwworm has moved so far northward in recent months, U.S. officials are increasingly concerned about the risk to border states like Texas.
—Brandi D. Addison, Austin American Statesman, 2 July 2025
Examples are automatically compiled from online sources to
show current usage.
Read More
Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
Send us feedback.
Isabel Mateos, Fortune, 25 July 2025
Here’s what to know about screwworms and how Texas plans to eradicate the pests.
—Brayden Garcia, Fort Worth Star-Telegram, 23 July 2025
The screwworm first became a significant problem in the United States in 1933, according to the USDA.
—Elizabeth Weise, USA Today, 10 July 2025
After a devastating 1972 outbreak in six states — California, Arizona, New Mexico, Texas, Oklahoma and Arkansas — the United States worked with Mexico to largely eradicate the screwworm.
—Bay Area News Group, Mercury News, 11 July 2025
So far the screwworms have only been seen in Mexico.
—Elizabeth Weise, USA Today, 10 July 2025
But the process of defeating the screwworm may not be quick — or inexpensive.
—Kameryn Griesser, CNN Money, 9 July 2025
With the resurgence of the screwworm, several types of animals are banned from import into the U.S. from Mexico, including:
live cattle
horses
bison
Screwworms life cycle
Where are screwworms located?
—Joyce Orlando, Nashville Tennessean, 13 May 2025
Because the screwworm has moved so far northward in recent months, U.S. officials are increasingly concerned about the risk to border states like Texas.
—Brandi D. Addison, Austin American Statesman, 2 July 2025
Cite this Entry
“Screwworm.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/screwworm. Accessed 3 Aug. 2025.
Copy CitationKids Definition
screwworm
noun
screw·worm
ˈskrü-ˌwərm
: the larva of a blowfly of the warm parts of America that develops in the wounds or sores of mammals and may cause disease or death
also
: the blowfly itself
Medical Definition
screwworm
noun
screw·worm
ˈskrü-ˌwərm
1
: either of two dipteran flies of the genus Cochliomyia:
a
: one (C. hominivorax) of the warmer parts of America whose larva develops in sores or wounds or in the nostrils of mammals including humans with serious or sometimes fatal results
especially
: its larva
2
: a dipteran fly of the genus Chrysomya (C. bezziana) that causes myiasis in Africa and southern Asia
Love words? Need even more definitions?
Merriam-Webster unabridged
Share