The Bee Bench › Brood Disease ID
Dead or sick brood, side by side: when it dies, what it looks like, whether it ropes, and what to do next. Includes the look-alikes that aren't disease at all — chilled, starved, poisoned and bald brood.
Pull the frame, find the dead or sick brood, and go down the list. Stop at the first one that fits.
Scroll sideways on a phone. The rope test and the scale are what separate AFB from everything else.
| Condition | Dies when | Capped? | Color | Feels like | Rope test | Scale | Smell |
|---|---|---|---|---|---|---|---|
| American Foulbrood (AFB) | After capping — prepupa or pupa | Yes. Cappings sunken, dark, greasy, often pierced | Dull white, then coffee, then dark brown | Soft, sticky, glue-like | Ropes 2 cm or more and snaps back | Flat on the lower cell wall, black, will not come out | Foul, like old glue (not always) |
| European Foulbrood (EFB) | Before capping — usually 4 to 5 day old larvae | Mostly open cells; a few sunken cappings in bad cases | Dull white, then yellow, then brown; white breathing tubes may show | Melted, twisted, slumped out of position | Weak — 1.5 cm at most, often none | Rubbery, twisted, easy to remove | Sour, vinegary (not always) |
| Sacbrood | After capping — stretched-out prepupa | Yes. Cappings may have one or two holes | Pale yellow, then brown to black, head first | A bag of watery, grainy fluid | No | Dry, brittle, boat-shaped, easy to remove | None |
| Chalkbrood | Around capping — mostly just-capped larvae | Often uncapped by the bees; mummies in open cells | White, turning grey to black as the fungus fruits | Hard, dry, chalk-like mummy | No | Loose mummy that rattles when you shake the frame | None, maybe slightly musty |
| Stonebrood | Before or after capping | Either | Yellow-green powdery coat | Rock hard, won't crush | No | Hard mummy, stuck or loose | None |
| Parasitic Mite Syndrome (PMS) | Many ages, open and capped | Both; cappings chewed or pierced | Off-white to light brown | Slumped and melted, like EFB | No (a little at most) | Rubbery, easy to remove | None to faint |
| Chilled brood | Every age in one patch, all at once | Both | Grey to black | Soft, then dries | No | Easy to remove | None to slight |
| Starved brood | Open larvae first | Mostly open | Dull white, drying | Dried and shrunken | No | Dry, easy to remove | None |
| Pesticide kill | Any age, suddenly | Both | Varies | Varies; larvae may crawl out of their cells | No | — | None |
| Bald brood | Usually survives | Cappings removed in a line | Normal — purple-eyed pupae showing | Healthy | No | None | None |
Bacteria — Paenibacillus larvae (spore-forming)
What you see: Spotty, shotgun brood pattern with sunken, pierced cappings scattered through it. Sometimes a dried pupal tongue sticks up from the scale toward the top of the cell.
Gets mistaken for: EFB (ropes less, dies before capping) and PMS (doesn't rope, mites present).
What to do: Close the hive, don't move frames or honey to other colonies, and reduce the entrance so nothing robs it. Confirm with a field kit or lab sample and call the state apiary inspector. Infected combs and frames are burned — the spores last for decades. Antibiotics only hide AFB, they never cure it, and in the US they need a veterinarian's order.
Bacteria — Melissococcus plutonius
What you see: Larvae twisted like a corkscrew or lying up the side of the cell instead of in a neat white C. Worst in spring, in colonies short on nurse bees or food.
Gets mistaken for: PMS looks almost the same — do a mite wash. Also AFB and sacbrood.
What to do: Often clears once the nectar flow picks up. Help it along: requeen (the brood break helps), feed, swap out old dark comb, or shake the bees onto new foundation if it's bad. Send a sample if you can't rule out AFB.
Virus — sacbrood virus
What you see: Larva lying on its back with the dark head raised toward the cell opening — the canoe or Chinese-slipper shape. Lift it with tweezers and it comes out whole, like a little bag of water.
Gets mistaken for: AFB (sacbrood doesn't rope) and EFB.
What to do: No treatment. Usually shows up in spring and fades on its own. If it hangs on for several brood cycles, requeen.
Fungus — Ascosphaera apis
What you see: Mummies in the cells, on the bottom board, and dumped out front. Worst at the edges of the brood nest in cool, damp spring weather.
Gets mistaken for: Stonebrood (rock hard, yellow-green powder) and packed pollen (flat, colored, not larva-shaped).
What to do: A stress sign. Improve ventilation, tip the hive slightly forward so it drains, give it sun, keep the colony strong, and requeen with hygienic stock if it keeps coming back.
Fungus — Aspergillus flavus / A. fumigatus
What you see: Mummies like chalkbrood but hard as stone and dusted with yellow-green spores. Rare. Can infect adult bees too.
Gets mistaken for: Chalkbrood.
What to do: Wear a dust mask — the same Aspergillus can make people sick if they breathe the spores. Remove and replace the affected comb and keep the colony strong and dry. Rare enough that a lab confirmation is worth having.
Varroa mites and the viruses they carry
What you see: Spotty brood, slumped larvae, chewed-open cappings with pupae showing. Adults with crumpled wings. Mites on bees and in drone brood. Late summer and fall, when mite loads peak.
Gets mistaken for: EFB and AFB. A mite wash settles it.
What to do: Do a mite wash — it will be high. Treat now. A colony this far along may not recover, so combine it if it's weak.
Not a disease — too few bees to keep the brood warm
What you see: A patch of dead brood of every age, usually at the edge of the brood nest, after a cold snap, a split, or a long inspection. Healthy brood right next to it.
Gets mistaken for: Foulbrood — but chilled brood kills every age at once and doesn't spread.
What to do: Nothing to treat. Don't make splits too small, keep cold-weather inspections short, and let the bees clean it out.
Not a disease — no food coming in
What you see: Shriveled larvae in open cells, bees pulling them out and dumping them. No honey or pollen near the brood. Eggs may disappear. Often in a dearth or right after a split.
Gets mistaken for: EFB.
What to do: Feed syrup and pollen substitute now. Check the rest of the yard — a dearth hits every hive.
Not a disease — poisoning
What you see: Dead and twitching adults piled at the entrance along with dead brood, all at once. Can hit several hives in one yard on the same day.
Gets mistaken for: Any brood disease — the sudden pile of dead adults out front is the giveaway.
What to do: Photograph it, freeze a zip bag of the dead bees as a sample, and report it to the PA Department of Agriculture. Move or cover the hives if spraying nearby is still going on.
Wax moth larvae tunnelling under the cappings
What you see: A straight or wandering row of uncapped cells with healthy pupae showing, following a moth tunnel. Silk threads under a magnifier.
Gets mistaken for: Chewed cappings from mites, or bees uncapping sick brood.
What to do: Usually minor. Keep the colony strong and it cleans it up.
Push a matchstick or twig into a suspect cell, stir, and pull it out slowly. AFB strings out 2 cm or more and snaps back like a rubber band. EFB may string a little and break. Nothing else ropes. Burn the stick afterward.
Lateral flow kits for AFB and EFB (sold by beekeeping suppliers) give an answer in a few minutes from a single larva. Good for confirming a yes. A lab is still the final word.
The USDA Bee Research Lab in Beltsville, MD tests brood samples for free. Cut a piece of comb about 2 by 2 inches with as many sick larvae as you can, no honey, wrap it in newspaper or a paper towel, and mail it in a small box. Never plastic, foil, or a zip bag — the sample rots and can't be tested. Check the lab's website for the current address and form.
Pennsylvania Department of Agriculture apiary inspectors will come look at no charge. With anything that might be foulbrood, call them. It protects every hive within flying distance of yours.