The saddest sight a beekeeper can see is a huddle of dead bees, heads thrust deep inside empty wax cells, with the queen dead in the middle. And the wretched thing is that they had starved just an inch away from a broad, golden arc of honey. This phenomenon is called “Isolation Starvation“.
That’s the scene I observed on Saturday, helping another beekeeper with their hives. When we lifted the hive, it was heavy with honey stores. But the bees had not been able to move up to the food, given the chill temperature. I think that we will see a lot of this upsetting sight this Spring – leading to abnormally high losses of bee colonies. Here’s why.
The combination of a long, mild Autumn and the wringing wet Winter has created conditions in the hive which are ideal for isolation starvation. The warm months of October, November and December allowed queen bees to continue laying eggs for longer. This encouraged the bees to fly to forage largely for pollen and, to a lesser extent, for nectar. With the brood nest still taking up room in the middle of the hive, newly-arrived honey had to be stored away from the centre. This has potentially severe consequences.
The size of the colony will have dwindled naturally as the days grew shorter (70,000 bees in summer falls to 10-15,000 in winter) and last Autumn’s extra activity accelerated the shrinking of the colony through attrition, as honeybees’ wings, beating at 13,500 strokes per minute, wore out from the extended foraging season. Varroa and nosema can also reduce bee numbers at this time of year, when colonies are naturally at their smallest – and therefore at their least heat-retentive. Even the application of anti-varroa treatments can eliminate a few more valuable bees…
When the weather turned colder 10 days ago, the bees started clustering tightly together, forming a heat-ball at the core of the hive, with the Queen at its centre. Here’s the problem: that’s precisely where the now-empty cells vacated by recently-hatched bee brood and the honey and pollen used by the nurse bees to feed them are located. A few inches away is an arch of rich honey. But now this seasonally smaller sphere of bees has been squeezed in the middle of the hive which has become a nursery unit, not a larder, as it should be. And sub-zero temperatures exert a constricting grip on the bee-bundle.
So despite a feast of honey just a fingertip away, the ball of bees contracts ever tighter, with the outer bees dying of cold and hunger, sometimes falling to the floor, but mostly head-down in the comb, immobilized by cold where they took the last lick of nutrition from that cell. That’s why isolation starvation is a special danger this winter.
If the weather turns warmer before the bees have been wiped out, isolation starvation can avoided: the bees can break their cluster, reorganise and move up to the food (bees will always move higher) and feed their Queen. There’s hope – but the weather is in the lap of the gods.
Even if you were a beekeeper reading this article and were worried about isolation starvation in your colonies, there’s not much a beekeeper can do about it at this stage. Preparing the hives for winter with plentiful food, appropriate space and good insulation is the best defence. Normally, if you heft your hives and they’re full of honey, with the bees are clustered deep in the frames, that’s reassuring. But if you feared isolation starvation for any reason and opened hives in today’s sub-zero temperatures to check, you would risk breaking the cluster, which many not be able to reform, as bees fall into a chill coma below 10C. That would lead to death. And even if you did pull out a comb to find a handful of half-starved bees, the usual rescue strategy of spraying them with warm sugar syrup would have little chance of working in a cold hive. Isolation starvation is a silent, invisible assassin.
Bee colony losses in 2014-2015 were just under 15%, 50% up on the previous year, according to the British Beekeepers Association (BBKA). With conditions so propitious for isolation starvation, I suspect this year’s overwintering losses will be higher yet.
Sad to say.