Corn rootworm, often called “the billion dollar bug,” is considered the greatest insect pest threat corn growers face. Damage from corn rootworm outpaces that from every other invertebrate pest combined by more than 80 million bushels, according to Crop Protection Network’s 2024 Corn Invertebrate Loss report.¹
Both larval and adult cornworm beetles damage corn. Larvae cause spring root damage, impeding water uptake and increasing risk of infection in seedlings.
Adults feed on leaves and silks in the summer, leading to poor pollination and reduced pollen set.
Corn rootworm have also developed resistance to several classes of insecticides, further increasing their ability to ravage corn yield.
Identifying corn rootworm
Managing corn rootworm starts with recognizing them. Here’s a guide to identifying corn rootworm species at different life stages.
Common species of corn rootworm
There are three common subgroups of corn rootworm: western corn rootworm (WCR), northern corn rootworm (NCR) and southern corn rootworm (SCR). Despite their names, today’s rootworms are widely distributed and not exclusive to these regions.
Western corn rootworm (Diabrotica virgifera virgifera)
Adult western corn rootworm (WCR) beetles are yellow or green and around 5/16” (7.5 mm) long. Easily misidentified as cucumber beetles, females have black stripes down the sides of their wing covers; males have stripes that are thicker, making their wing covers appear almost entirely black or of darker pigmentation. Female WCR adults have larger abdomens.²
Northern corn rootworm (Diabrotica barberi)
Adult northern corn rootworm (NCR) beetles are pale green or tan and about ¼” (6 mm) long. NCR beetles newly emerged from the pupal stage can be a lighter cream color. Females tend to be larger than males.
Southern corn rootworm (Diabrotica undecimpunctata howardi)
Though not as economically impactful as WCR and NCR, Southern corn rootworm (SCR) can still cause problems. SCR adults, often called spotted cucumber beetles, are about ⅜” (9 mm) long. Ranging from yellow to greenish, SCR beetles feature 11 distinct black spots on their backs.
Scouting for corn rootworm larvae and eggs
Though the adult forms of our three corn rootworm beetles are distinctive, their eggs and larvae are virtually identical across species. Eggs are small, cream-colored or white ovals. Females lay some 500 eggs over several weeks, around 80 eggs at a time. Eggs can be found in late summer around corn or soybean roots, typically in the upper 6” of soil, and remain dormant until the following spring.³
Corn rootworm larvae typically hatch in late May or early June if corn is present. Larvae are less than ½” long and white. Their dark head and dark brown tail plate make them appear “double-headed.” They have three pairs of legs, too small to see without magnification.
Corn rootworm larvae seek corn roots after hatching and feed on them for four to six weeks. Once they’ve stored enough nutrients, they dig a cell in the soil and pupate.
Scouting for corn rootworm adults
Adult corn rootworm beetles typically appear in late June or early July. Males emerge first, followed by females five to seven days later. Within two weeks of emergence, adults have mated and the females begin laying eggs, with peak egg laying occurring around mid-August.
Adults can typically be found feeding on corn silks, pollen, leaves and kernels. Scout weekly from mid-July to early September to determine infestation intensity. If you count more than one adult beetle per corn plant in the field, expect economic impact from yield loss and increased egg laying in upcoming seasons.4
Experts are available to help you make corn rootworm management decisions. Reach out to your seed retailer, a nearby extension office agent, or your regional BASF representative.
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Endnotes
- “Corn Invertebrate Loss Estimates from the United States and Ontario, Canada — 2024.” Crop Protection Network, 17 Feb. 2025, cropprotectionnetwork.org/publications/corn-invertebrate-loss-estimates-from-the-united-states-and-ontario-canada-2024. Accessed 22 Jan. 2026.
- “Corn Rootworms.” Purdue University - College of Agriculture, 29 July 2025, ag.purdue.edu/department/entm/extension/field-crops-ipm/corn/corn-rootworms.html. Accessed 22 Jan. 2026.
- “Corn Rootworm.” Extension & Outreach, Crop Sciences Department, University of Illinois, 2023, extension.cropsciences.illinois.edu/fieldcrops/insects/corn_rootworm/. Accessed 22 Jan. 2026.
- Wangila, David S., et al. “Considerations for Managing Corn Rootworm — It’s Not Too Late.” CropWatch, University of Nebraska-Lincoln, 10 July 2025, cropwatch.unl.edu/considerations-managing-corn-rootworm-its-not-too-late/. Accessed 22 Jan. 2026.
