Not all bee ailments arrive with the drama of American Foulbrood or the relentless creep of Varroa. Some are quieter — gut parasites that shorten lives by weeks, viruses that twist wings, mites that live inside breathing tubes like tiny, suffocating nightmares. These are the afflictions of the margins, the ones that tip a struggling colony into collapse or whittle away at a strong one until it is merely average.
Let us catalog them, not to terrify, but to equip you. Knowledge is the beekeeper's best prophylactic.
Nosema is caused by two species of microsporidian fungi: Nosema apis and Nosema ceranae. Both infect the midgut of adult bees, multiplying inside the cells that line the intestine, impairing digestion and shortening lifespan. The result is a bee that cannot properly process food, loses weight, and dies prematurely — often after defecating uncontrollably, hence the common name "bee dysentery."
Symptoms: Nosema-infected colonies exhibit increased mortality, especially in late winter and early spring. You may see bees with distended abdomens, unable to fly, crawling weakly near the entrance. The front of the hive, the landing board, and the top bars may be streaked with brownish fecal stains — bees normally defecate only on cleansing flights outside the hive, so this is a red flag.
Inside the hive, population dwindles. The queen's laying slows because infected workers produce less royal jelly. The colony enters a death spiral: fewer bees, less food for the queen, fewer new bees, and so on.
Diagnosis: Definitive diagnosis requires a microscope. Crush a sample of bees (ideally 30 or more), macerate them in water, and examine the liquid under 400x magnification. Nosema spores are oval, refractile, and unmistakable once you know what you are looking for. Many state apiary labs will test samples for free.
Treatment: Fumagillin (sold as Fumidil-B) is the only approved medication in the United States, and it is controversial. It suppresses nosema but does not cure it — spores remain in the hive. Some studies suggest fumagillin can harm bees' immune systems, potentially doing more harm than good. Many beekeepers have abandoned it in favor of management strategies:
Nosema ceranae, the newer of the two species, does not always produce visible dysentery, making it harder to detect but no less damaging.
Honeybees are hosts to dozens of viruses, most of which cause no apparent harm under normal conditions. But when bees are stressed — by mites, poor nutrition, or environmental extremes — viral infections can explode.
Deformed Wing Virus (DWV) is the most visible. Bees infected as pupae emerge with crumpled, useless wings, unable to fly. They crawl around the entrance or are dragged out by workers and left to die. DWV is vectored primarily by Varroa mites — the mites' feeding introduces the virus directly into the bee's hemolymph (blood). High mite loads correlate directly with high DWV prevalence. Control Varroa, and you control DWV.
Chronic Bee Paralysis Virus (CBPV) causes trembling, hairlessness, and a dark, greasy appearance in infected bees. They lose the ability to fly and are often attacked by their nestmates, who recognize them as sick. CBPV spreads through direct contact, so crowded colonies with poor hygiene are most at risk.
Sacbrood Virus kills larvae just before pupation. The dead larva's body fills with fluid, forming a sac-like structure inside the skin. Workers remove these infected larvae, and the colony usually recovers on its own if the population is strong. Requeening can help if sacbrood persists.
There are no antiviral treatments for bees. The only defenses are maintaining strong, well-fed colonies with low mite loads and good genetics.
Tracheal mites (Acarapis woodi) are microscopic parasites that live inside the bees' breathing tubes (tracheae), feeding on hemolymph and impairing respiration. Infected bees struggle to fly, often exhibiting "K-wing" — wings held at odd angles, unable to fold properly. They die prematurely, unable to forage effectively.
Tracheal mites cannot be seen without a microscope and a dissection. You must remove a bee's head, isolate the thoracic tracheae, and examine them under magnification for the tiny, pale mites clustered inside.
Fortunately, tracheal mites are far less common now than they were in the 1980s and 1990s. Many modern bee stocks carry genetic resistance. The best prevention is to purchase bees from reputable breeders who select for resistance. If you suspect an infestation, menthol crystal treatments (placed on top bars in warm weather) can help, though results are inconsistent.
Notice the pattern? Nearly every ailment in this chapter is worsened by stress and mitigated by strength. Nosema hits hardest in late winter when bees are clustered and food is scarce. Viruses explode when Varroa weakens immune systems. Tracheal mites thrive when bees are already struggling.
The solution is not to chase every disease with a different chemical. The solution is to build resilient colonies:
Strong colonies do not avoid disease — nothing does. But they resist disease, often shrugging off infections that would kill a weak hive.
"The best disease treatment is the one you never have to apply, because your bees are healthy enough not to need it."
— Randy Oliver, ScientificBeekeeping.com
If you see crawling bees, fecal staining, or deformed wings in small numbers, monitor but do not panic. Every colony has a baseline level of disease. If you see these symptoms increasing week after week, or if more than 5% of your bees are affected, it is time to act.
Test for Varroa. Check food stores. Inspect the brood pattern. Consider requeening. And if symptoms persist or worsen despite your interventions, consult an experienced beekeeper or your state apiary inspector. Sometimes the problem is not what you think it is, and a second set of eyes can save a colony.