Bees are disappearing because of several threats hitting them simultaneously: parasites, pesticides, habitat loss, poor nutrition from monoculture farming, and climate change. No single factor explains the decline on its own. During the winter of 2024-2025, an estimated 40.2% of managed honey bee colonies in the United States were lost, and wild bee species face even steeper pressures with fewer safety nets.
Colony Collapse Isn’t One Problem
Colony Collapse Disorder, or CCD, became a household term in the mid-2000s when beekeepers started finding hives suddenly empty of adult bees. Scientists have spent years trying to pin down a single cause, and the short answer is there isn’t one. A comprehensive survey published in PLoS One analyzed 61 variables across affected colonies, including bee physiology, pathogen loads, and pesticide levels, and no single measure emerged as the most likely culprit.
What researchers did find was that collapsing colonies carried far more infections than healthy ones. Bees from CCD colonies were co-infected with an average of 4.3 known pathogens, compared to 3.0 in healthy colonies. Co-infection with four or more viruses was 3.7 times more common in collapsing hives. Co-infection with two species of the gut parasite Nosema was 2.6 times more common. The pattern suggests that something weakens bees first, and then infections finish them off.
Varroa Mites: The Leading Parasite
The Varroa destructor mite is widely considered the single greatest biological threat to Western honey bees. These tiny parasites latch onto bees and feed on their fat reserves, but the real damage comes from what they carry. Varroa mites are confirmed biological vectors for multiple viruses, meaning the viruses actively replicate inside the mites before being transmitted to bees. Research published in the Journal of Virology identified at least eight viruses replicating within the mites, including two strains of deformed wing virus, the pathogen most closely linked to colony deaths.
Varroa weakens the bee immune system while simultaneously flooding the hive with viral infections. A mite-infested colony faces a compounding problem: bees become less able to fight disease at the exact moment they’re being exposed to more of it. For beekeepers, managing Varroa is a constant battle that requires monitoring and treatment throughout the year.
How Pesticides Disrupt the Bee Brain
Neonicotinoids are a class of insecticides used on crops, lawns, ornamental plants, and even flea treatments for pets. They work by targeting the nervous system of insects, binding to receptors that handle a key signaling chemical in the brain. In bees, this disrupts two abilities they cannot survive without: smell and navigation.
When exposed to neonicotinoids at concentrations found in real agricultural settings, bees lose the ability to distinguish between different odors. Research on bee brain activity shows that exposure causes the neural “maps” bees use to identify specific scents to collapse into near-identical patterns. A bee that can’t tell one flower smell from another can’t forage efficiently, can’t communicate food locations to the hive, and can’t learn which flowers are worth revisiting. The same brain regions affected by these chemicals also process visual information used for navigation, which helps explain why exposed bees often fail to return to their hives.
The damage doesn’t have to be lethal to be devastating. Chronic, low-level pesticide exposure weakens the immune system, making bees less able to fight off the infections already circulating in their colonies. This is one of the key interactions researchers suspect drives colony collapse: pesticides don’t kill bees outright, but they leave them vulnerable to everything else.
The U.S. Environmental Protection Agency has taken several steps in response. It has prohibited certain neonicotinoid applications when bees are present, halted approval of new outdoor neonicotinoid uses pending updated risk assessments, cancelled residential turf spraying of imidacloprid (one of the most common neonicotinoids), and proposed label language advising homeowners against using these products. The European Union has gone further, banning outdoor use of three major neonicotinoids entirely.
Monocultures and Malnutrition
Modern agriculture has replaced diverse landscapes with vast stretches of single crops. For bees, this creates a feast-or-famine situation. A thousand acres of almonds or canola may provide abundant nectar for a few weeks during bloom, but once that crop finishes flowering, the landscape becomes a food desert. The conversion to monoculture farming is a primary driver of declining floral diversity and abundance, which directly impacts both wild and managed bee populations.
Bees need a varied diet, just like humans do. Pollen from different plant species provides different nutrients, and a diverse diet supports a stronger immune system. When bees are limited to a single pollen source, or face gaps between blooms with nothing available at all, their nutrition suffers. Research has linked this suboptimal nutrition to compromised immune function and poor overall colony health. It’s another piece of the same pattern: nutritional stress doesn’t kill bees directly, but it makes them less resilient to parasites, viruses, and chemical exposure.
Climate Change and Timing Mismatches
Rising temperatures are shifting the biological calendars of both plants and pollinators, but not at the same rate. A study in the Proceedings of the National Academy of Sciences found that for every 4°C increase in long-term average temperature, flowering advanced by about 14 days. Generalist bees, which visit many flower types, advanced their activity by about 17 days per 3.2°C of warming. That may sound roughly proportional, but specialist bees, those that depend on specific plants, shifted by only 8 days per 1.7°C of warming.
These mismatches matter. When a bee emerges from hibernation or begins foraging before its food plants have bloomed, it faces starvation during a critical period. When flowers bloom and no pollinators are active yet, both the plant and the bee lose out. Over time, these timing gaps can destabilize the relationships between specific plants and their pollinators, particularly at northern latitudes where temperature shifts are most pronounced.
Wild Bees Face Even Greater Risk
Most public attention focuses on honey bees, which are a managed, non-native species in North America. But there are thousands of native bee species, many of them solitary ground-nesters, that face the same threats with none of the human support. A 2025 analysis in PNAS found elevated extinction risk in over one-fifth of native North American pollinators.
The primary threats to wild bees are agriculture, climate change, and housing and urban development. Unlike managed honey bees, which can be moved to new locations, fed sugar syrup during shortages, and treated for mites, wild bees depend entirely on their local habitat. When that habitat is paved over, plowed under, or stripped of floral diversity, wild bee populations have no fallback. Some species rely on specific plants to complete their life cycles, so the loss of even a single plant species from a landscape can eliminate the bees that depend on it.
Why It Matters for Food
Over 75% of globally important crop types benefit from animal pollination, including fruits like apples, stimulant crops like coffee, and oilseeds like sunflower. About 18% of average national crop consumption across 163 countries comes from animal-pollinated crops. Without pollinators, an estimated 3 to 8% of total crop consumption would be lost entirely. That may sound modest in percentage terms, but it represents some of the most nutritionally valuable and economically important foods in the human diet: fruits, vegetables, nuts, and seeds.
What Actually Helps Bees
The most effective thing you can do in your own yard or community is increase floral diversity. Plant a range of species that bloom at different times throughout the growing season, so bees have continuous access to food rather than a brief burst followed by nothing. Native plants are particularly valuable because local bee species evolved alongside them.
Habitat structure matters as much as flowers. About 70% of native bee species nest in the ground, and they need bare, uncompacted soil to do it. Leaving small patches of exposed earth in your garden, using stepping stones instead of solid pavement for walkways, and reducing mulch coverage in some areas all create potential nesting sites. Even a small patch of bare soil next to a container plant can serve as a nest location.
Research from the University of Georgia has shown that naturalistic green spaces, such as parks and gardens that mimic natural ecosystems, support greater bee diversity than formal, heavily managed flower beds. The takeaway is counterintuitive for many homeowners: a slightly wilder, less manicured landscape is often better for bees than a perfectly tended garden. Reducing or eliminating pesticide use on your property, particularly neonicotinoid-based products often sold for lawn care and ornamental plants, removes one of the stressors bees face in residential areas.