If you are new to beekeeping, the list of things that can go wrong reads like a medical textbook, and it is easy to lie awake worrying about all of them at once. Here is the calming truth about bee health: most colony losses are preventable, and they trace back to a short list of causes rather than the whole encyclopedia of bee pathogens. A strong colony fends off most of it on its own. Varroa is the one threat you have to actively manage, and a quick look at the brood pattern tells you early when something is off.
This guide sorts the threats to your colony by how much they should actually worry you. It starts with the one habit that prevents most problems, keeps varroa brief and points you to the full guide for the how-to, then walks the brood diseases from serious to manageable. If you are just getting oriented, the beekeeping for beginners guide is a good companion to this one.
The one rule: strong colonies stay healthy
Almost everything about bee health comes back to one idea: a strong colony resists most pests and diseases without your help. Strong means eight or more frames of bees, a young laying queen, a low varroa load, and clean comb. Give the bees those four things and their own defenses do the heavy lifting.
Those defenses are real and well studied. Bees practice hygienic behavior, detecting and pulling out diseased larvae before an infection spreads. They coat the hive in propolis, which has antimicrobial properties, and they groom and remove the dead.
A queen mated with many drones gives the colony genetic diversity that makes it more resilient. Most experienced beekeepers requeen with hygienic stock every year or two to keep all of this working.
The scale of the losses shows why it matters. US beekeepers lost 55.6 percent of managed colonies in the 2024 to 2025 season, the highest annual loss since national surveys began, with varroa and the viruses it spreads among the leading drivers. That number is frightening, but much of it comes down to mite management, which means much of it is preventable.
Your single best diagnostic is free and takes seconds. A healthy brood frame is solid and compact, with capped cells packed tightly together. A spotty, scattered pattern with sunken or discolored cells is the earliest warning of most brood diseases. Read that pattern at every visit and you will catch trouble while it is still small.
Varroa mites: the one you must actively manage
If you do only one active health job all season, make it varroa. Varroa destructor is a parasitic mite that feeds on the fat bodies of your bees and spreads viruses, above all deformed wing virus. It is the leading cause of colony loss worldwide, and nearly every colony has some level of infestation.
The goal is to keep the load low, since wiping mites out entirely is not realistic. The common threshold is to act at around three mites per hundred bees, and late summer is the critical window, because that is when a rising mite load damages the bees that need to carry the colony through winter. Deformed, shriveled wings on young bees mean the virus load is already high and a mite program has fallen behind.
Varroa earns a full guide of its own, so this section stays brief. The complete walkthrough on how to monitor mites and choose a treatment lives in the varroa mites guide. Mites are also the main reason strong-looking colonies collapse over winter, so winter beekeeping success comes down to your late-summer mite numbers.
Brood diseases: which to fear and which to manage
Brood diseases sound alarming as a group, but they are not equally serious, and the difference is worth learning. The brood pattern is again your signal: a spotty frame with odd-looking caps or larvae is your cue to look closer. Reading it well is a core inspection skill, covered in the beehive inspection guide.
American foulbrood is the serious one, and it is the only bee disease that should genuinely scare you. Caused by the bacterium Paenibacillus larvae, it kills larvae after the cells are capped, leaving sunken, greasy, perforated caps and a foul smell. The classic tell is the ropy test: a matchstick pushed into a dead cell and drawn out slowly pulls a brown, mucus-like string one to three centimeters long.
Its spores survive for decades in equipment, there is no practical cure, and it is legally reportable in many states, so check what your own state requires. If you suspect it, stop, do not move frames or equipment that could spread spores, and call your state apiary inspector, because the standard response is destroying and burning the affected colony.
European foulbrood is the milder cousin and is far more manageable. It kills larvae before capping, leaving twisted, yellow-brown larvae curled in open cells and a sour smell, and it fails the ropy test. It often clears on its own during a strong nectar flow, and beekeepers generally help it along by requeening with hygienic stock and improving nutrition.
Chalkbrood is the least worrying of the three. It is a fungus that leaves white or grey chalky mummies, often visible on the landing board or the hive floor. It rarely kills a colony, favors cool damp conditions, and usually resolves as the weather warms and the colony strengthens.
Nosema and the other adult-bee problems
Not every problem shows up in the brood. Nosema is a gut disease of adult bees that appears as a slow spring build-up and a dwindling population. Two species cause it and they do not behave the same way. Nosema apis is the one classically linked to brown dysentery streaking on the front of the hive, while Nosema ceranae, now the more common of the two across much of the United States, often leaves no visible streaking at all, which is part of why it goes unnoticed. A 2020 proposal reclassified both species into the genus Vairimorpha, so you will see them written either way, though that revision is still disputed among bee scientists. Either way it needs a lab test to confirm, since the symptoms overlap with other stresses. Strong, well-fed colonies with low varroa rarely show symptoms, which is why beekeepers generally find that good management does more here than any chemical.
The other adult-bee threats are mostly viruses, and this is where everything loops back to mites. Varroa carries and amplifies deformed wing virus and several others, so for practical purposes, controlling those viruses means controlling mites. That is one more reason the varroa program sits at the center of colony health rather than off to the side.
Hive pests: beetles, moths, and mice
Some threats are opportunists that move in when a colony is weak. The pattern holds here too: a strong colony defends against all three, while a weak or queenless one is vulnerable.
The small hive beetle tunnels through comb and ferments the honey, giving off a smell like rotting oranges. Strong colonies corral the beetles into cracks and coat them in propolis, but a weak or queenless colony can be overrun in days. Oil traps set between frames help, though a strong colony is the best defense.
Wax moths leave silk webbing and dark frass that ruin comb. They target weak colonies and, especially, stored frames that no bees are guarding, and they rarely trouble a healthy hive. The standard prevention for stored comb is to freeze frames for 48 hours at 0F, which kills the eggs and larvae before they can spread.
Mice and robbers are a seasonal problem. A reduced entrance in autumn keeps out mice looking for a warm winter home, and it also helps your guard bees fend off robbing bees and wasps when forage runs short.
The habits that prevent most problems
None of this requires constant intervention. A handful of steady habits prevents the large majority of what kills colonies, and most of them are things you would do on a normal inspection anyway. Folding them into a hive management rhythm is what keeps small problems from becoming losses.
- Keep colonies strong and well fed, with a young, productive queen.
- Monitor varroa several times a season and treat based on the numbers, not the calendar.
- Read the brood pattern at every inspection: solid is healthy, spotty is a warning.
- Replace old dark comb every two to three years to reduce spore and residue build-up.
- Clean your hive tool between colonies, by flame or alcohol, and never feed honey from an unknown source.
- Call your state apiary inspector for suspected American foulbrood or any unexplained multi-colony loss, since most offer free help.
That last point matters. State apiarists are a resource for your hobby, and they would much rather hear from you early than find a spreading outbreak later.
The bottom line
Keep your colonies strong, manage varroa on the numbers, read the brood pattern, and act early. Those four habits handle the vast majority of what actually kills colonies, and they turn a frightening list of pathogens into a manageable routine. Most brood diseases are either mild or self-limiting, and the pests mostly prey on weakness you can prevent. None of it asks for daily attention, only a steady eye during the inspections you already run.
Reserve your sharpest caution for two situations: anything that looks like American foulbrood, and any loss across several colonies that you cannot explain. In both cases, stop and call your state inspector before you move equipment around. Strong bees and a careful eye on the brood catch nearly everything else. Since varroa is the one active job on that list, the best next step is the varroa mites guide, where the monitoring and treatment details live.
Frequently asked questions
What is the biggest threat to honey bees?
The varroa mite, both directly and through the viruses it spreads, above all deformed wing virus. It is the leading cause of colony loss worldwide, and managing it is the single highest-impact thing a beekeeper does. Nearly every colony has mites, so the goal is to keep the load low, since zero is not achievable.
How do I know if my colony is sick?
Read the brood pattern first. A solid, compact pattern signals health, while a spotty pattern with sunken, greasy, or discolored cells is the early warning for most brood diseases. Also watch for deformed wings, crawling bees, dysentery streaks on the hive front, and a sudden foul or sour smell during an inspection.
What is the difference between American and European foulbrood?
American foulbrood is the serious, reportable one: it kills larvae after capping, passes a ropy string test, and its spores survive decades, so infected colonies are usually burned. European foulbrood kills larvae before capping, fails the ropy test, is far milder, and often clears on its own during a strong nectar flow.
Can I prevent bee diseases?
You cannot eliminate all risk, but strong colonies, a young hygienic queen, clean comb, low varroa, and early action prevent most losses. A large, healthy population with a productive queen is the best defense there is, because the bees do most of the disease control themselves when you keep them in good shape.
Sources and further reading
Bee health touches animal disease, some of it legally reportable, so these are the references worth reading directly.
- Honey Bee Health Coalition, Tools for Varroa Management, the standard free US and Canadian guide to sampling and treating the mite behind most colony losses.
- Penn State Extension, American foulbrood, on identifying and handling the disease that is reportable in many states.
- USDA Agricultural Research Service (2025), on miticide-resistant mites, the viruses they spread, and recent colony collapses.
Disease rules and treatment labels vary by state and change over time, so confirm anything actionable with your state apiarist or local club.