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
The Food and Drug Administration is working to authorize the emergency use of some drugs and pesticides to treat or prevent New World screwworm infections.
—
Clara Migoya, AZCentral.com, 23 Sep. 2025
Brazilian beef faces a 76% tariff, and the USDA has blocked livestock from Mexico to the U.S. due to concerns over the screwworm parasite.
—Brittney Melton, NPR, 22 Sep. 2025
The bacteria does not technically eat tissue like screwworms do.
—N'dea Yancey-Bragg, USA Today, 28 Aug. 2025
The Agriculture Department has said screwworms have been making their way north into Mexico from other parts of Central America.
—Patrick Smith, NBC news, 25 Aug. 2025
How do screwworms affect cattle and other livestock?
—Bloomberg, Mercury News, 25 Aug. 2025
It was largely eradicated for decades in the U.S. through a technique in which male screwworm flies are sterilized and then released into the environment to mate with females until the population dies out.
—Youri Benadjaoud, ABC News, 25 Aug. 2025
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Clara Migoya, AZCentral.com, 23 Sep. 2025
Brazilian beef faces a 76% tariff, and the USDA has blocked livestock from Mexico to the U.S. due to concerns over the screwworm parasite.
—Brittney Melton, NPR, 22 Sep. 2025
The bacteria does not technically eat tissue like screwworms do.
—N'dea Yancey-Bragg, USA Today, 28 Aug. 2025
The Agriculture Department has said screwworms have been making their way north into Mexico from other parts of Central America.
—Patrick Smith, NBC news, 25 Aug. 2025
How do screwworms affect cattle and other livestock?
—Bloomberg, Mercury News, 25 Aug. 2025
It was largely eradicated for decades in the U.S. through a technique in which male screwworm flies are sterilized and then released into the environment to mate with females until the population dies out.
—Youri Benadjaoud, ABC News, 25 Aug. 2025
Cite this Entry
“Screwworm.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/screwworm. Accessed 29 Oct. 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
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