The small, bee-like insects you see swarming around corn tassels are almost certainly not bees at all. They’re hover flies, also called syrphid flies, and they’re one of the most commonly misidentified insects in cornfields. Some people call them “corn bees” or “sweat bees,” but they belong to an entirely different group: true flies, not bees. That said, real bees do interact with corn in important ways, and cornfields pose some serious risks to nearby pollinators.
What “Corn Bees” Actually Are
Hover flies mimic the appearance of bees and wasps so convincingly that even experienced gardeners mistake them. The species most commonly seen on corn tassels belong to the genus Toxomerus, and they feed on pollen. They hover in place near the plant, which adds to the bee illusion, but a closer look reveals key differences: hover flies have only two wings (bees have four), their antennae are short and stubby, and their eyes are disproportionately large for their head, more like a housefly than a honeybee.
These flies are completely harmless. They don’t sting, and they’re actually beneficial. Their larvae, which look like small, plain maggots, feed on pollen that collects in the leaf axils and other crevices of corn plants. Some hover fly larvae also eat aphids, making them a natural pest control agent. If you’re seeing clouds of these insects around your corn, there’s nothing to worry about and no reason to spray.
Why Real Bees Visit Cornfields
Corn is wind-pollinated, so it doesn’t produce nectar to attract bees. But it does produce enormous quantities of pollen, and bees will collect it as a protein source for their colonies. Honeybees, bumblebees, and various wild bee species all forage on corn tassels when other pollen sources are scarce. This is especially common in late summer in agricultural regions where corn dominates the landscape and wildflower diversity is low.
Young corn seedlings also produce guttation droplets, those small beads of water that form at leaf tips in the early morning. Bees sometimes drink from these droplets, which becomes a problem when the corn was grown from pesticide-treated seed. The insecticide is taken up by the plant’s vascular system and concentrates in guttation fluid at levels far higher than what appears in pollen or nectar.
How Corn Farming Threatens Bees
The biggest risk to bees from corn isn’t the crop itself but the pesticides applied to it, particularly a class of insecticides called neonicotinoids. The vast majority of corn seed planted in the U.S. is coated with neonicotinoids before it ever goes in the ground. These chemicals are systemic, meaning the growing plant absorbs them into every tissue, including pollen and the guttation fluid bees drink.
The toxicity is staggering when you look at the numbers. The lethal dose for a honeybee exposed to clothianidin (one of the most common corn seed treatments) is just 22 to 44 nanograms through skin contact and as little as 2.8 nanograms if ingested. A single treated corn kernel contains enough active ingredient to kill over 80,000 honeybees. The question isn’t whether these chemicals are dangerous to bees. It’s how much exposure bees actually get in real-world conditions.
Planting Dust
One major exposure route happens at planting time. Seed-planting equipment uses talc or graphite as a lubricant to keep treated seeds flowing smoothly through the machinery. This lubricant picks up neonicotinoid residue from the seed coatings and gets expelled into the air through the planter’s exhaust. The contaminated dust can drift onto flowering plants near the field, where foraging bees contact it directly. Research has found that bee-attractive plants within about 165 feet (50 meters) of a cornfield being planted are vulnerable to this dust drift. Investigations of bee die-offs near cornfields during planting season have found neonicotinoid traces in dead and dying bees and high levels in their stored pollen.
Guttation Droplets
The guttation fluid from seedlings grown from treated seed contains neonicotinoid concentrations that are orders of magnitude higher than what’s found in pollen. Researchers measuring these droplets found concentrations as high as 346 parts per million for imidacloprid, 102 ppm for clothianidin, and 146 ppm for thiamethoxam. For context, the levels found in pollen and nectar of treated plants are typically below 0.01 ppm. Guttation concentrations are highest on the first day after seedlings emerge, can dip over the following week, and then often spike again. Drier soil conditions push concentrations even higher, with one measurement reaching over 1,100 ppm under dry conditions.
These droplets appear on corn leaves in the early morning hours, exactly when bees are beginning to forage and seek out water sources.
Why Regulation Has Been Slow
One reason neonicotinoid-coated seeds have avoided stricter oversight is a regulatory gap. Under federal pesticide law, treated seeds are classified as “treated articles” and are exempt from EPA registration requirements, as long as the pesticide used on the seed itself is registered. This means the seed product doesn’t undergo the same risk assessment that a sprayed pesticide would. The EPA completed proposed interim review decisions on the major neonicotinoids in January 2020, suggesting label changes to reduce pollinator exposure, but these proposals did not result in any mandatory label changes.
Protecting Bees Near Cornfields
If you keep bees or want to support pollinators near agricultural land, several practical steps can reduce the risk. Communication is the starting point. Tools like FieldWatch and BeeCheck allow beekeepers to register hive locations so that nearby growers and pesticide applicators can see where hives are and plan accordingly.
Timing matters significantly. Pesticide applications made after bees stop foraging for the day, typically around 6:00 to 7:00 PM during summer, carry much lower risk than midday spraying. Growers can also reduce planting dust by following manufacturer recommendations for seed lubricant quantities and by avoiding planting on windy days.
Creating alternative habitat around cornfields makes a meaningful difference for pollinators over time. Planting diverse wildflower patches that bloom throughout the season gives bees food sources beyond corn pollen. Hedgerows with blooming shrubs and trees, non-crop buffer strips, and restored native plant areas all help. For ground-nesting bees (which make up the majority of wild bee species), leaving patches of untilled bare soil or grass provides nesting sites. Clean water sources like birdbaths, irrigation ditches, or ponds give bees alternatives to guttation droplets.
When establishing a pollinator planting, choosing a seed mix with high species diversity and staggered bloom periods ensures pollen and nectar availability across the entire growing season. In the first year, mowing once when plants reach about 24 inches tall, but no shorter than 10 to 12 inches, helps the planting establish by suppressing weeds while protecting the pollinator-friendly species underneath.