A dead colony: working out what happened

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Seal it before you start

A dead colony is an undefended box of honey. Dead colonies attract robbers fast, and robbing is one of the ways disease moves from hive to hive. 2 So block the entrance and shut every gap.

Look at the brood before you move anything. If it makes you suspect foulbrood, the box stays exactly where it is and nothing leaves the site, because the duty to report starts on suspicion and the ban on moving hives, combs, bee products and appliances starts with it. 4 That is the next two sections, and they are worth reading before you lift the box rather than after.

Clear of that, get the box off the site and work through it somewhere you can shut the frames away again.

The signs that mean stop

Look at the brood first. Both foulbroods are notifiable, and it is suspicion that starts the duty, not certainty. Nobody diagnoses either one by eye, inspectors included.

• American foulbrood is in the sealed brood. Cappings go dark and sunken, some moist or greasy, perforated with jagged off centre holes. Under a dark slimy capping the remains draw out on a matchstick as a brown thread 10 to 30 mm long. The last stage is a very dark, rough scale on the lower wall of the cell. 3
• European foulbrood is mainly in the unsealed brood. Larvae turn yellow, twist in the cell and look melted. They dry to a brown scale with a rubbery feel that lifts out of the cell easily.

A dead colony has no fresh brood, so the field test for European foulbrood may not be possible. American foulbrood scales you can hunt yourself. Use a light source, hold the comb at about 45 degrees, and look down into the cells for scales on the lower wall. 1

What the law actually asks

In England the duty sits in the Bee Diseases and Pests Control (England) Order 2006. It falls on an owner or person in charge of a hive who knows or suspects that bees from it are infected with a notifiable disease. That person shall “immediately notify that fact to the Secretary of State”. Notifiable disease means American foul brood or European foul brood. A hive means any thing that contains, or has at any time contained, a colony of bees. 4

Once you have notified, the Order stops you removing hives, bees, combs, bee products, hive debris or appliances from those premises. You may still send samples to the Secretary of State for laboratory testing. That is the legal wording for do not clear it up. Failing to comply is an offence, and the fine on summary conviction is at level 5 on the standard scale, which has been unlimited in England and Wales since March 2015. Do not read across from the old five thousand pound figure. 5

Contact the National Bee Unit on nbu@apha.gov.uk or 0300 303 0094, and put your own standstill on the apiary. Inspection is free, and a standstill notice runs for a minimum of six weeks. 6 Wales, Scotland and Northern Ireland have their own orders. Varroa and foulbrood: what UK law asks of you has the rest.

Isolation starvation

A common February answer, and the hardest to take, because the food was in the box. The bees eat the stores out on one side and the cluster ends up marooned away from the rest. Hefting does not show it. 7 The checks that do catch it in time are in Spotting starvation, and emergency feeding.

What it leaves is a small cluster in the middle of the hive, with stores only in the outside frames. The bees are head down in the cells. 1 A big colony would have walked across to those combs. A small cluster in cold weather cannot.

The other marks are dry cells where the brood nest was, and dead bees piled deep enough to block the entrance. There may be nibbled cappings over healthy looking pupae, but those prove nothing on their own. Foulbrood, heavy varroa and chilled brood all produce them too. Ivy honey sets very hard, so a colony can also die on heavy stores it was never able to soften. Autumn feeding covers getting the weight in beforehand.

Varroa and virus collapse

This one looks like the bees walked out. The National Bee Unit lists four signs of collapse. 9

• The adult bees drop away sharply, and usually there are few dead adults to show for it.
• Some of the bees left behind have deformed wings and short abdomens.
• Mites in numbers: on the adult bees, in worker and drone pupae, and down on the floor.
• Brood left to die as it emerges, in patches, browned and half pulled out by the bees.

So the tell is what is not there. Stores still capped, a handful of bees, and no bodies. Collapse is usually rapid, and in the UK it is most common in August and September. The death can be months older than the winter it gets blamed on.

A bee that emerges with deformed wings dies within two or three days, so a few in the floor debris matter more than they look. Uncontrolled mites may not kill a colony in the first year, but they can bring it down after two or three. 8 The August treatment decides this one.

Queenless going into winter

A queenless colony rarely gets through winter. The cluster holds its heat less well, and no queen means no young bees to take over from the workers in spring. Below about 9,000 bees, roughly three full British Standard frames of bees, the odds are poor. Five frames covered is the sensible minimum. 10

In the post mortem, no dead brood at all is a fairly clear case of queen failure. The queen stopped laying months ago, no new bees came through, and the old ones died of old age. 1

If she turned drone layer instead, you get domed cappings on worker cells. Laying workers leave much the same picture, and the two are not easy to tell apart. Laying workers give a patchy pattern, eggs on the cell walls as well as the base, and sometimes more than one egg to a cell. 11 Either way it was settled in October, and the last proper look before winter is where it gets caught.

Robbed out

An empty box does not prove starvation. Look at the rims of the cells that should have held stores. If they are ragged and torn, and there is a lot of wax debris on the floor, the colony was probably robbed. That happens either after it died, or while it was too short of bees to defend itself. 1

What survives robbing is the bodies. Robbers take stores, not corpses. So a cluster of bees head down in the cells still points at starvation, whatever the comb looks like. Wasps do the same job from outside, and wasps at the hive covers keeping them out.

Damp

It is the damp rather than the cold that kills bees. A colony makes a lot of water vapour and it condenses on the cool hive walls, so the box has to shed it. Roof, entrance and floor ventilation is normally enough. Tilting the hive very slightly forwards or leaving the floor insert out helps. 10

The evidence is a wet hive, not a mouldy one. Anything dead since December will have mould on the combs, so mould by itself tells you nothing. Standing water on the floor, sodden frames, a soaked cluster and a split in the roof tell you a great deal.

How much ventilation a hive wants is genuinely contested among beekeepers. Insulation over the crown board against open top ventilation has been argued about for decades. The fact sheet puts insulation where the winters are hard, and asks that good ventilation is kept up if you use it.

Nosema and dysentery

Brown streaking down the front of the hive, over the top bars and across the combs is dysentery. It is a sign, not a diagnosis. Chronic bee paralysis virus, nosema, amoebic disease and unsuitable stores such as fermented or coarsely granulated sugars all produce it. 12

Nosema is only confirmed under a microscope, by crushing about 30 abdomens and looking at 400 times magnification. Then be careful what you conclude. A National Bee Unit survey of over 5,000 colonies in 2010 and 2011 found 46% carrying Nosema apis and 40% carrying Nosema ceranae, with no strong correlation between either and poor colony health.

Nosema ceranae is the one that shows itself. Dead bees outside the hive, bees crawling in the grass, abnormally small adults, and a colony that dwindles in spring instead of building. In a dead hive, faecal smears are worth a line in the record and not much more.

What to do with the equipment

What you can keep depends entirely on the answer above.

• Foulbrood suspected or confirmed: nothing moves and nothing gets cleaned until an inspector has seen it. Brood frames that have touched either foulbrood are burned, and zinc slotted queen excluders go the same way. Wooden equipment burns in a pit about 45 cm deep, covered over afterwards so nothing can get at unburnt honey. American foulbrood spores stay viable for decades, and acetic acid does not touch them. 13
• Starvation, queen failure, damp or robbed out: the woodwork and most of the comb are fine. Melt down any frame with dead bees or brood on it, and wash the frame in a hot washing soda solution before it goes back into service. 1
• Wax moth in the combs: nearly always a consequence rather than the cause. Wax moth destroys unoccupied comb in colonies that are weak, queenless, starving or diseased. Scrape the cocoons off, seal the frames in bags, and freeze them for 48 hours to kill every life stage. 15 Storing supers has the rest.
• Nosema: acetic acid fumigation disinfects comb that has been contaminated with Nosema apis, but it may not be effective against Nosema ceranae. It is hazardous, and freezing is the safer choice where it will do. 14

For anything else, and for any second-hand kit, scrape it clean first, because wax and propolis stop a disinfectant working. Then scorch wooden boxes to a uniform dark brown, or submerge plastic and polystyrene parts in 0.5% sodium hypochlorite for twenty to thirty minutes. 2 Hive tools, and keeping them clean has the mixes.

Write down what you found while the frames are in front of you, including what you could not settle. Next winter that note is the only record you will have.