Many reports of caterpillars feeding at the tips of corn ears have prompted discussions about how to distinguish between common ear-feeding caterpillars. In particular, western bean cutworm infestations across the state have been misidentified as corn earworm, probably because of the location of feeding and western bean cutworm being an infrequent pest in Iowa. Here are some tips to help you distinguish the two caterpillars. Regardless of species, if caterpillars or their injury are found in corn, continue to monitor the field for ear molds prior to harvest.
Western bean cutworm
Western bean cutworm is an infrequent, native pest of corn and dry beans. There is one generation per year and they overwinter in a pre-pupal stage in the soil. Moths emerge in late spring or early summer and lay eggs on host crops.
Larvae start out very small and purple with black heads. As they grow, their bodies turn tan with stripes running the length of the body, and their heads turn orange. Older, larger larvae are tan or gray in color and lack stripes, but they are easily distinguished by two dark rectangles behind the head. Western bean cutworm larvae do not have raised bumps (tubercles) or hairs on the body and appear generally smooth and granular, similar to other cutworm species. Several larvae can be present in a single ear.
Western bean cutworm larvae feed on many parts of the corn plant, depending on the crop growth stage. In vegetative corn, small larvae will feed in the uppermost leaves on tassel tissues. After tasseling, larvae may be found in the leaf axils feeding on pollen and anthers. They will also move to the ear, feeding on silks, the ear tip, cob tissue, and developing kernels. They may also enter the side of the ear to feed on kernels.
*If you guessed western bean cutworm from Rebecca's photo, you're correct!
Corn earworm
Corn earworm is a native pest of corn, cotton, tomatoes, and many other crop species. They are not known to overwinter in Iowa and instead migrate from more southern areas each summer. There may be multiple generations of corn earworm in Iowa, depending on the timing of first arrival. Moths lay eggs on fresh corn silks upon arrival.
Corn earworm larvae have an orange head and alternating light and dark stripes along the body at all larval stages. Color is not a reliable characteristic for corn earworms, since they can appear green, yellow, brown, purple, and black. Corn earworm larvae are covered in tubercles and hairs, which can be less obvious as they mature. Corn earworm larvae are cannibalistic, so usually only one larva is present in an ear.
Corn earworm larvae exclusively feed on the ears in corn. Small larvae will feed on silks as they travel down the silk channel into the ear. Usually, corn earworm larvae feed on kernels and tissues at the ear tip. Occasionally, they may follow a silk channel to the middle of the ear and feed there.
A side-by-side comparison
If you find caterpillars but you can't tell what it is, you can reach out to Ashley, Erin, or your local ISU field agronomist for confirmation.
Management strategies are not discussed here because it is too late in the growing season for insecticide applications according to research-based recommendations. Correct identification of caterpillars can help you understand whether current management strategies, like Bt hybrids, were effective and the need for future management of the pest.
Use the resources below to learn more about life cycles, scouting, and management of these pests.
Ecology and Management of the Western Bean Cutworm (Lepidoptera: Noctuidae) in Corn and Dry Beans – Revision with Focus on the Great Lakes Region. Journal of Integrated pest Management, 2019.
Pest Status and Management of Corn Earworm (Lepidoptera: Noctuidae) in Field Corn in the United States. Journal of Integrated Pest Management, 2019.
Recognizing feeding injury to corn ears in the United States. Journal of Integrated Pest Management, 2024.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on August 15, 2025. The information contained within may not be the most current and accurate depending on when it is accessed.
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