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How to identify it
- Full-grown caterpillars vary a lot in color: green, yellow, pink, red, tan, maroon, brown or nearly black, with paler or darker stripes along the body. UC IPM and Clemson put their length at about 1 1/2 inches; Wisconsin says up to 2 inches.[1][2][5][3]
- The head is plain, without spots: brown according to Kentucky, yellow according to Wisconsin.[1][2]
- The skin is covered with tiny spines that make older caterpillars feel rough to the touch; a hand lens shows them best.[1][4]
- The moth spans about 1 to 1 1/2 inches. Males are usually light yellowish olive and females yellowish brown to pinkish brown, each forewing has a dark spot near the center, and the hind wings are dull white with a dark gray band near the edge.[1][4][5]
- Eggs are tiny (about 1/32 inch), round and ribbed, and laid one at a time. They are white or cream when laid and develop a reddish brown ring after about a day.[4][5][2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Fall armyworm | A fall armyworm has a pale, upside-down Y on the front of its head and sometimes four black dots on the back of each abdominal segment. A corn earworm's head is unmarked, and its skin is covered with tiny spines.[6][1] |
| Tobacco budworm | A close relative that is very hard to tell apart as a caterpillar without magnification; the youngest caterpillars can't be separated at all. The adult moths can usually be told apart by wing color.[7] |
Where it lives
It occurs throughout the Western Hemisphere, from Canada to Argentina. Pupae can survive the winter only up to roughly the 40th parallel; farther north they die from spending too long at near-freezing temperatures. In Wisconsin few survive the winter, and most earworms there come from moths that fly north from the Gulf States, so late-summer flights are the damaging ones. GBIF has about 13,500 U.S. records since 1990, most from Texas, then Colorado, Oklahoma, Illinois, Missouri, Ohio, Indiana and Wisconsin.[3][8][2][9][10]
Biology and life cycle
The moths are most active in the evening and at night. Females lay single eggs on leaves and especially on fresh corn silk, and Wisconsin says each female can lay up to 1,000 eggs.[5][1][2]
Hatch time depends on temperature. Wisconsin gives 1 to 8 days and says eggs can hatch within 24 hours in hot weather; UC IPM gives 5 to 7 days for sweet corn.[2][5]
The caterpillars are cannibals, so you rarely find more than one in an ear or a fruit.[1][2][3]
Caterpillars finish feeding in about two weeks (14 to 16 days in Kentucky), drop to the ground and pupate 1 to 9 inches deep in the soil. The moth comes out about two weeks later, so a generation takes about 30 days in midsummer.[1][2]
Kentucky usually sees about four overlapping generations a year, with egg-laying moths around for most of the season.[1]
Damage and signs
- In corn, young caterpillars feed on the silks, clipping them off, then move into the tip of the ear and eat kernels, leaving a mess of droppings. The damaged tip also draws sap beetles.[5][2][1]
- In tomatoes, young caterpillars bore in at the stem end, preferring green fruit, and leave a messy, watery cavity full of droppings and shed skins. Damaged fruit ripens early, and one caterpillar may move through several small fruits.[4][3]
- Numbers build as summer goes on: UC IPM says it is most abundant in August and September, and Kentucky says late-season sweet corn is at greatest risk.[5][1][4]
- A 2016 review found that it has become a much bigger problem in U.S. sweet corn over the past two decades.[11]
Health risk
The extension sources describe it only as a pest of corn, tomatoes and other crops. The harm is to the harvest: ruined ear tips and tomatoes.[1][4][3]
Control
Prevention
Plant sweet corn early. Early and midseason plantings face fewer moths and need fewer treatments than corn that silks in late summer.[1][5]
Varieties with long, tight husks tend to get less damage than those with loose husks.[1]
Biological control
Trichogramma wasps and other parasites kill many eggs, and minute pirate bugs, lacewings and damsel bugs eat eggs and small caterpillars. Parasitized eggs usually turn black, so check for them before spraying tomatoes.[4][5][2]
An organic option described by Wisconsin Extension combines Bt with vegetable oil in a single applicator; timed correctly, it can give 80 to 90 percent control.[2]
Pesticides
Treat at egg hatch, while caterpillars are still on the silks or leaves. Once they are inside the ear or fruit, sprays can't reach them. In corn, start when silks first appear.[5][1][2][4]
Bt and spinosad are acceptable for organic growing. Some earworm populations in the Midwest resist pyrethroids, the class most often used on sweet corn.[4][5][1][2]
Common questions
- How much of the ear does an earworm ruin?
- Usually just the tip. The caterpillar stays near the end of the ear, but it eats kernels and fouls the tip with droppings, so damaged tips are usually cut off, and the damage draws sap beetles.[2][5][1]
- Are corn earworm and tomato fruitworm the same insect?
- Yes. Helicoverpa zea is called corn earworm, tomato fruitworm or cotton bollworm, depending on the crop.[3][2]
- Why doesn't spraying my corn stop earworms?
- Newly hatched caterpillars move down the silks into the ear within a day or so, where sprays can't reach them. Spraying only helps when it is timed to egg hatch, and late-season corn needs the most protection.[1][5][2]
Sources
- University of Kentucky Entomology, “ENTFACT-318: Corn Earworm Management in Sweet Corn (R. Bessin, rev. 1/26).” entomology.ca.uky.edu/ef318 (accessed 2026-11-11)
- University of Wisconsin-Extension, “Corn earworm (A3655, Delahaut, Cullen and Wedberg).” hort.extension.wisc.edu/files/2014/11/A3655.pdf (accessed 2026-11-11)
- Clemson Cooperative Extension, Home & Garden Information Center, “Tomato Insect Pests (HGIC factsheet).” hgic.clemson.edu/factsheet/tomato-insect-pests/ (accessed 2026-11-11)
- University of California Statewide IPM Program, “Tomato Pest Management Guidelines: Tomato Fruitworm.” ipm.ucanr.edu/agriculture/tomato/tomato-fruitworm/ (accessed 2026-11-11)
- University of California Statewide IPM Program, “Corn Earworm (Corn Pest Management Guidelines).” ipm.ucanr.edu/agriculture/corn/corn-earworm/ (accessed 2026-11-11)
- NC State Extension, “Fall Armyworms in Turf.” content.ces.ncsu.edu/fall-armyworm-in-turf (accessed 2026-11-11)
- NC State Extension, “Tobacco Budworms.” content.ces.ncsu.edu/tobacco-budworms (accessed 2026-11-11)
- Environmental Entomology, via PubMed, “Cold hardiness of Helicoverpa zea pupae (Morey et al. 2012).” pubmed.ncbi.nlm.nih.gov/22525073/ (accessed 2026-11-11)
- Global Biodiversity Information Facility (GBIF), “Helicoverpa zea: U.S. occurrence records since 1990 by state (GBIF occurrence search).” api.gbif.org/v1/occurrence/search?taxonKey=1792564&country=US&hasGeospatialIssue=false&occurrenceStatus=PRESENT&year=1990%2C2026&facet=stateProvince&facetLimit=400&limit=0 (accessed 2026-11-11). Exact count at access: 13,451 U.S. records since 1990 (Texas 4,013; Colorado 1,053; Oklahoma 957; Illinois 919; Missouri 465; Ohio 355; Indiana 354; Wisconsin 341).
- Global Biodiversity Information Facility (GBIF), “Helicoverpa zea: occurrence records since 1990 by country (GBIF occurrence search).” api.gbif.org/v1/occurrence/search?taxonKey=1792564&hasGeospatialIssue=false&occurrenceStatus=PRESENT&year=1990%2C2026&facet=country&limit=0 (accessed 2026-11-11). Exact counts at access: 14,567 records since 1990; United States 13,451, Canada 733, Brazil 140, Mexico 123, Argentina 28.
- Journal of Economic Entomology, via PubMed, “Biology, Ecology, and Evolving Management of Helicoverpa zea in Sweet Corn in the United States (Olmstead, Nault and Shelton 2016).” pubmed.ncbi.nlm.nih.gov/27329622/ (accessed 2026-11-11)
- iNaturalist, “Helicoverpa zea taxon page (order and family).” www.inaturalist.org/taxa/118492 (accessed 2026-10-06)