What does armyworm mean?
An armyworm is the caterpillar of certain noctuid moths, notorious among farmers for feeding in large, mobile groups that can strip a field of grasses or grain crops with alarming speed. The name reflects the insects' behavior: like an advancing army, the larvae move en masse from one food source to the next, consuming leaves, stems, and seed heads as they go. Several distinct species carry the name, including the African armyworm (Spodoptera exempta) and the fall armyworm (Spodoptera frugiperda), the latter having spread from the Americas into Africa and Asia where it devastates maize harvests. The word appears almost exclusively in agricultural, scientific, and pest-management contexts, usually preceded by a species qualifier. Though unremarkable as individual caterpillars, armyworms are memorable collectively — a single infestation can reduce a thriving crop to stubble within days.
nounThe caterpillar of various noctuid moths that moves in destructive groups and feeds voraciously on grasses, grain crops, and other plants; also the moth itself in some contexts.
- The destructive caterpillar larva of certain noctuid moths (notably Spodoptera species), which feeds on grasses and crops and often moves in mass groups.
- By extension, any of the moths whose larvae are known as armyworms.
"Farmers watched helplessly as an advancing armyworm stripped their wheat fields bare overnight."
"The fall armyworm has become one of the most damaging invasive pests of maize in sub-Saharan Africa."
"Entomologists tracked the migration of the moths to predict where the next generation of armyworm larvae would emerge."
Standard pluralization; used when referring to multiple individuals or mixed species of these pests.
"The pesticide was effective against both cutworms and armyworms."
Named for its habit of marching across farmland like a ravenous invading force, a single armyworm outbreak can devour an entire field's crops almost overnight.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of armyworm
The word armyworm is an English compound formed from "army" and "worm." The element "army" derives through Old French "armée" from Latin "armata," meaning an armed force, while "worm" comes from Old English "wyrm," tracing back to Proto-Germanic *wurmiz, a word distantly related to Latin "vermis" (whence vermin and vermicelli). The compound arose in English agricultural usage, likely in the 18th century or earlier, to describe the caterpillars' habit of moving across fields in massed groups resembling an invading host. Related descriptive names such as cutworm were coined along similar lines for other noctuid larvae.
Related word forms
How armyworm is actually used
Chiefly used in agricultural, entomological, and pest-control contexts rather than everyday speech. The name is applied to several distinct species (e.g., African armyworm Spodoptera exempta, fall armyworm Spodoptera frugiperda), so writers often prefix it with a modifier identifying the specific kind.
Easily confused with armyworm
Cutworms are related noctuid caterpillars that typically feed at soil level by cutting down seedlings, whereas armyworms feed openly on foliage and march across fields in large groups.