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How to identify it
- Full-grown caterpillars are about 1 1/2 inches long (Iowa State says up to 2 inches) and range from green and yellow to brown, gray or nearly black, with pale stripes along the body.[1][3][4][2]
- The key mark is a pale, upside-down Y on the front of the head.[1][3][2]
- Up close, four black dots may show on the back of each abdominal segment, and the largest caterpillars have a reddish-brown head and raised dark spots.[3][5]
- Newly hatched caterpillars are only about 1/8 inch, greenish with a black head.[5][4]
- The moths are gray with white markings and a wingspan of about 1 to 1 1/2 inches; the forewing has a pale, drop-shaped mark or white spot near the center.[1][3]
- Egg masses are cream to tan with a fuzzy, moldy look and turn up on grass blades and on posts, siding, playground sets, bird feeders and golf carts.[1][4][5]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| True armyworm | The true armyworm is the commonest lawn armyworm in Utah; its caterpillars are yellow or gray with black stripes, sometimes pinkish, and its moth is reddish-brown with a distinct white dot in the center of each wing. NC State says fall armyworms are harder to control.[6][3] |
| Cutworms | Cutworms clip leaf blades close to the crown and leave small, scattered pockets of damage, while armyworms feed in masses and leave larger irregular brown patches.[6] |
Where it lives
Native to the tropics and subtropics of the Western Hemisphere. In the United States it doesn't survive prolonged freezing and overwinters only in southern Texas and Florida; moths fly north each year and reach most of the country east of the Rocky Mountains and into eastern Canada. Since 2016 it has also invaded Africa, Asia and Oceania.[7][8][9][10][11]
Biology and life cycle
Moths fly north from the Gulf states through spring and summer; NC State traces North Carolina's turf infestations to Florida, and storms can blow huge numbers of moths as far as Iowa in late August.[3][1][4][9]
A female can lay up to 1,000 eggs, Clemson says in a single night, in masses that Iowa State puts at 100 to 500 eggs. Eggs hatch in 2 to 10 days, and the young caterpillars spin silk threads that help them disperse.[1][3][4]
Caterpillars feed for 2 to 3 weeks (NC State) or 3 to 4 weeks (Iowa State), eating most of their food in the last larval stages, then pupate in the thatch or soil; moths emerge 10 to 20 days later.[3][5][1]
The whole cycle can take about a month, so there can be three or more generations a year in South Carolina and several in North Carolina.[1][3]
Caterpillars can feed day or night but are most active in early morning and late afternoon or evening, hiding in the thatch in bright sun.[3][1][2]
Damage and signs
- Early feeding on turf looks like drought stress; later feeding leaves a scorched or scalped look with only grass stems left, often with a sharp line between damaged and green turf that spreads out from posts or buildings where eggs were laid.[1][3]
- Bermudagrass and tall fescue are favored, and most grasses can be hit, along with corn, sorghum and small grains. New sod and new seedings under a year old suffer most.[1][3][4]
- Because the caterpillars eat blades rather than roots or crowns, lawns usually recover with watering, though thin areas may need reseeding.[2][4][6]
Health risk
The fall armyworm is a pest of grasses and crops; the extension sources here describe it only as a threat to lawns, turf and crops.[1][3]
Control
Prevention
Check suspect areas with a soap flush: mix 1 to 2 tablespoons of lemon-scented dish detergent in 1 to 2 gallons of water and pour it over a square yard of healthy grass next to the damage. Armyworms come up within about 10 minutes.[1][6]
Traps and physical control
Scrape or brush egg masses off siding, posts and play sets, or scrub them with soapy water; spraying insecticide on egg masses does nothing.[4][5]
Biological control
Lady beetles, parasites and other natural enemies often keep fall armyworms in check, though cold, wet springs make them less effective and they can't stop a large outbreak.[3]
Pesticides
Treat only if caterpillars are still small; large ones are about to stop feeding and are hard to kill. Mow and water lightly first, spray early or late in the day, and avoid watering for 24 hours afterward. Bt and spinosad work best on small larvae.[3][4][1][6]
Clemson lists bifenthrin, cyfluthrin, cypermethrin, lambda-cyhalothrin, permethrin or spinosad. Iowa State notes reports of pyrethroid resistance and suggests switching to chlorantraniliprole or tetraniliprole if a pyrethroid doesn't work quickly.[1][4][5]
The 2021 outbreak
In 2021 fall armyworms badly damaged turf from Oklahoma to Georgia and Indiana to Maryland between June and August, and storms carried moths into Iowa, where egg masses turned up on siding, posts and vehicles.[5][4]
Kentucky called it one of the worst years on record for fall armyworms in home lawns, unusual because they hit cool-season grasses that they normally leave alone. A frost ends the problem, since they don't overwinter that far north.[2][5]
A migrant pest worldwide
Genetic markers show two U.S. source populations: moths from Texas reach as far as Pennsylvania and eastern Canada, and Texas and Florida migrants mix routinely north of South Carolina.[9][10][8]
The fall armyworm was first reported in West Africa in 2016 and spread across Africa and most of Asia within two years. Genome studies find the invaders belong to the corn strain, which suggests limited potential to infest rice.[11][7][12]
Where sources disagree
Egg numbers: Clemson says a moth can lay up to 1,000 eggs in a single night and NC State gives as many as 1,000, while Iowa State describes masses of 100 to 500 eggs.[1][3][4]
Grass preference: Utah State says armyworms prefer cool-season turfgrasses, Kentucky calls cool-season lawns an unusual target, and Clemson names bermudagrass and tall fescue as the usual hosts.[6][2][1]
Size: most sources give about 1 1/2 inches for a grown caterpillar, Iowa State 1 1/2 to 2 inches, and an Iowa State article 1 1/3 inches.[1][3][4][5]
Common questions
- How do I tell armyworm damage from drought?
- Early armyworm damage looks like drought stress. Look for caterpillars feeding in early morning or late evening, or pour a soap flush beside the brown area to bring them up.[1]
- Why do armyworms show up in late summer?
- They don't survive winter in most of the country. Moths fly north from southern Texas and Florida each year, so numbers build as the summer goes on.[8][1][3]
- Will my lawn come back?
- Usually. The caterpillars eat blades, not roots, so keep the lawn watered; reseed thin spots, ideally in fall, and fertilize lightly to speed recovery.[2][4][6]
- Should I spray the fuzzy egg masses on my house?
- No. Insecticides don't control the eggs; scrape them off or scrub them with soapy water.[5][4]
Sources
- Clemson Cooperative Extension Home & Garden Information Center, “Armyworms: Identification, Damage, & Control in Turfgrass (HGIC 2159, updated July 15, 2025).” hgic.clemson.edu/factsheet/armyworms-identification-damage-control-in-turfgrass/ (accessed 2026-11-11)
- University of Kentucky Martin-Gatton College of Agriculture, Food and Environment, “Brown lawns could mean fall armyworm damage (2021).” exclusives.mgcafe.uky.edu/2021/hort/brown-lawns-could-mean-fall-armyworm-damage (accessed 2026-11-11)
- NC State Extension, “Fall Armyworms in Turf.” content.ces.ncsu.edu/fall-armyworm-in-turf (accessed 2026-11-11)
- Iowa State University Extension and Outreach, Yard and Garden, “Fall Armyworm Control in Home Lawns (Aug. 30, 2021).” yardandgarden.extension.iastate.edu/encyclopedia/fall-armyworm-control-home-lawns (accessed 2026-11-11)
- Iowa State University Extension and Outreach, Yard and Garden, “Fall Armyworms: The Surprise of 2021 (Sept. 10, 2021).” yardandgarden.extension.iastate.edu/article/2021/09/fall-armyworms-surprise-2021 (accessed 2026-11-11)
- Utah State University Extension, “Armyworms and Cutworms in Turfgrass.” extension.usu.edu/planthealth/research/armyworms-and-cutworms-in-turfgrass (accessed 2026-11-11)
- Insects, via PubMed, “Genetic relationship of fall armyworm (Spodoptera frugiperda) populations that invaded Africa and Asia (2021).” pubmed.ncbi.nlm.nih.gov/34066149/ (accessed 2026-11-11)
- Ecology and Evolution, via PubMed, “Nagoshi, Meagher and Hay-Roe (2012), Inferring the annual migration patterns of fall armyworm in the United States from mitochondrial haplotypes.” pubmed.ncbi.nlm.nih.gov/22957154/ (accessed 2026-11-11)
- Environmental Entomology, via PubMed, “Nagoshi, Fleischer and Meagher (2009), Texas is the overwintering source of fall armyworm in central Pennsylvania.” pubmed.ncbi.nlm.nih.gov/20021748/ (accessed 2026-11-11)
- Frontiers in Insect Science, via PubMed, “Tessnow, Nagoshi, Meagher and Fleischer (2023), Revisiting fall armyworm population movement in the United States and Canada.” pubmed.ncbi.nlm.nih.gov/38469489/ (accessed 2026-11-11)
- Scientific Reports, via PubMed, “Yainna, Tay, Durand and others (2022), The evolutionary process of invasion in the fall armyworm (Spodoptera frugiperda).” pubmed.ncbi.nlm.nih.gov/36473923/ (accessed 2026-11-11)
- Scientific Reports, via PubMed, “Invasive fall armyworms are corn strain (2024).” pubmed.ncbi.nlm.nih.gov/38459145/ (accessed 2026-11-11)
- iNaturalist, “Spodoptera frugiperda taxon page (order and family).” www.inaturalist.org/taxa/132468 (accessed 2026-10-06)