Common Bee Diseases & Pests Guide: Identification & Treatment 2026

Q: What is American foulbrood and how do I identify it?

American foulbrood (AFB) is a bacterial disease (Paenibacillus larvae) that kills capped larval bees. Signs: sunken, discolored cappings (brown, dark); foul rotting smell; the 'ropiness' test — insert a matchstick into a capped cell, if it pulls out a stringy strand more than 1 inch long, AFB is likely. AFB is a nationally notifiable disease in most jurisdictions. If you suspect AFB, contact your provincial/state apiary inspector immediately — equipment must be destroyed by burning.

Q: What is the difference between American foulbrood and European foulbrood?

American foulbrood (AFB) kills capped larvae (after capping) and produces the characteristic ropy, sunken cappings — a severe disease requiring destruction of equipment. European foulbrood (EFB) kills uncapped larvae (before capping) — dead larvae appear twisted, yellow-brown, and have a sour smell rather than AFB's rotting smell. EFB is less severe: treatment with oxalic acid, requeening, and improving colony nutrition often resolves it without equipment destruction.

Q: What are small hive beetles and how do I control them?

Small hive beetles (SHB, Aethina tumida) are invasive beetle pests that lay eggs in honeycomb, causing larvae to tunnel through comb and contaminate honey with a fermented, slimy mess. Most common in warmer regions of North America. Control: maintain strong colonies (bees can police SHB themselves when strong), use SHB traps with vegetable oil (bees chase beetles into traps where they drown), keep floors clean, and avoid leaving weak or dead hives — SHBs thrive in unguarded comb.

Q: What does chalkbrood look like in a beehive?

Chalkbrood (Ascosphaera apis fungal infection) produces hardened, chalky-white or gray-black mummified larvae that are found on the bottom board or at the hive entrance as bees clean them out. A light case of chalkbrood (occasional mummies, strong colony) often resolves itself. Severe chalkbrood usually indicates stress: excess moisture, cold conditions, or a weak colony. Improve ventilation, reduce moisture, and consider requeening with hygienic behavior genetics — some queen lines are dramatically more resistant to chalkbrood.

Disease and pest management is the most challenging aspect of modern beekeeping. Bees face pressures they didn't face 50 years ago: Varroa mites (introduced to North America in 1987) weakened colony immune systems, opened the door to viral infections, and fundamentally changed beekeeping practice. Understanding what you're looking at during inspections is critical to responding appropriately.

Varroa Mites (Varroa destructor)

Varroa is the single greatest threat to honey bee colonies worldwide. The external parasitic mite feeds on bee larvae and pupae, transmits viral diseases (DWV, sacbrood), and causes colony collapse if untreated. Most colonies without treatment die within 2–3 years. Varroa is not "just a mite" — it is an existential threat to untreated colonies.

See our dedicated varroa mite treatment guide for the complete diagnostic and treatment protocol. The short version: test regularly with alcohol wash or sugar roll, treat when mite load exceeds 2 mites per 100 bees, use oxalic acid in late fall for maximum efficacy.

American Foulbrood (AFB) — The Most Serious Bacterial Disease

AFB is caused by Paenibacillus larvae spores that contaminate equipment and kill brood. It is legally reportable in most Canadian provinces and US states — if you suspect it, you are legally required to contact your provincial/state apiary inspector.

Identification:

Sunken, greasy-looking cappings that are darker than healthy (brown vs white)
Foul smell — rotting wood, often described as "nail polish remover" or acrid
The ropiness test: insert a twig or match into a suspect cell — AFB-infected material pulls out in a rope >1 inch long
Spotty, inconsistent brood pattern

Response: Do not treat — in most jurisdictions, all equipment from an AFB hive must be burned or irradiated. Contact your apiary inspector. The spores survive for 40+ years in equipment and cannot be eliminated by any safe home treatment. This is one of the few bee diseases where the correct response is destruction, not treatment.

The CFIA honeybee disease control resources provide Canadian regulatory requirements for AFB response.

European Foulbrood (EFB)

EFB is caused by Melissococcus plutonius and kills uncapped larvae. Less severe than AFB.

Identification:

Twisted, discolored (yellow to brown) larvae in uncapped cells
Sour milk smell (distinctly different from AFB's rotting smell)
Spotty brood pattern
Ropiness test NEGATIVE (does not pull like AFB)

Response: EFB often resolves with colony management. Requeen with hygienic behavior genetics, improve nutrition (protein patties), ensure adequate ventilation, and ensure strong colony population. In severe cases, a licensed veterinarian or apiary inspector can prescribe oxytetracycline treatment.

Chalkbrood

Fungal infection producing mummified larvae, found as chalky white or black mummies at the hive entrance or on the bottom board. Usually indicates colony stress (moisture, cold, weak population).

Response: Improve ventilation, reduce moisture, ensure strong colony population. Requeen with hygienic behavior genetics — the #1 long-term solution. Light chalkbrood in a strong colony often resolves without intervention.

Small Hive Beetles (SHB)

In warmer North American climates (Zone 7+), small hive beetles are a serious concern. They lay eggs in comb, contaminating honey with a slimy, fermented mess that smells of rotting oranges.

Control:

Keep colonies strong — bees chase SHBs into corners and prevent them from accessing comb
SHB beetle traps with vegetable oil — place in dark corners of hive, bees chase beetles in and they drown
Remove all dead or weak hives promptly — unguarded comb is SHB paradise
Plastic corrugated bottom boards: SHBs can hide in the corrugations; use screened bottom boards instead

For the complete hive inspection process where you'll watch for all these signs, see our hive inspection guide. For varroa specifically, our varroa treatment guide provides the complete testing and treatment protocol. For winter preparation that addresses mite loads, see our hive winterization guide.

Frequently Asked Questions

What is American foulbrood and how do I identify it?

American foulbrood (AFB) is a bacterial disease that kills capped larvae. Signs: sunken, discolored cappings; foul rotting smell; the ropiness test — insert a matchstick into a capped cell, if it pulls a string more than 1 inch long, AFB is likely. If you suspect AFB, contact your apiary inspector immediately — equipment must be destroyed by burning in most jurisdictions.

What is the difference between American foulbrood and European foulbrood?

AFB kills capped larvae (after capping) with ropy, sunken cappings — requires equipment destruction. EFB kills uncapped larvae (before capping) — dead larvae appear twisted, yellow-brown, with a sour smell. EFB is less severe: requeening and improving colony nutrition often resolves it without equipment destruction.

What are small hive beetles and how do I control them?

Small hive beetles lay eggs in honeycomb, causing larvae to tunnel through comb and contaminate honey. Control: maintain strong colonies (bees police SHB when strong), use oil traps, keep floors clean, and promptly remove dead hives. Most common in warmer climates (Zone 7+).

What does chalkbrood look like in a beehive?

Chalkbrood produces hardened, chalky-white or gray-black mummified larvae found on the bottom board or at the hive entrance. A light case in a strong colony often resolves itself. Severe chalkbrood indicates stress — excess moisture, cold, or weak colony. Improve ventilation and consider requeening with hygienic behavior genetics.