Drones are not the only bees that drift

Something has been vexing me about honey bees. Two observations, both true, seem to be in direct conflict with each other:

1. They are excellent navigators, able to roam far and wide, then return home with great accuracy
2. A high proportion of both drones and workers turn up in hives where they were not born, and queens regularly fail to return from their mating flights
   

Do bees drift more than you think? One of the first things we learn as beekeepers is that bees are great at finding their way home. When we first get bees we marvel at their orientation flights; hovering while facing the hive entrance, then flying in ever increasing spirals. We are told that, once bees have learned where their entrance is, we should not move the hive. One way to boost a small hive is to swap its position with a strong hive in the apiary. Many foragers from the strong hive end up in the weak one, which now occupies the place of their former colony. Many of my initial failures with mini mating nucs were caused by not moving them far away from the hives from which their bees were shaken; they just fly home leaving empty mating nucs. Yes, I know, schoolboy error. I make lots of them.

Liberal or Conservative Hives?

When I decide to shake out a hive with laying workers (or for other reasons) I remove the hive and dump the bees at least 10 metres away, often further. Very quickly I can see bees gathering at the entrances to other hives, begging their way in. A clump of bees will form at the site of their home (which is now gone) but often by the next day it is quite small, and most of them have relocated to neighbouring hives. So, without doing any fancy experiments, it is easy to see that some hives will allow bees from other hives to join them. I don’t know if the propensity to allow foreign bees in is a trait that varies between colonies; I suspect it might be. Perhaps some are more like Suella Braverman (UK Home Secretary) than others.

I can understand bees drifting to other hives when they have been shaken out and their home removed; they have little choice. However, they drift a lot more than many people realise even without such upheaval. Drones are serial drifters; they are a bit like cats in that they don’t really have a single owner, but they share themselves around several, depending on the rewards offered. Workers are at it too, however. I recently learned that when bees at the NBU hives were tested, a large swathe of workers (I can’t recall whether it was 66% or 34%) were in a different hive to the one in which they were raised. Is this deliberate or something to do with the way hives are lined up, barely a foot apart, all looking alike? Or a bit of both?

Natural and Artificial Spacing

I don’t know the answer, which is why I’m vexed. The movement of both workers and drones between hives is of concern when we consider the spread of disease and parasites. Beekeepers that line up ten or twelve hives in a row will often find that the ones at the ends of rows grow tall, whereas the central ones don’t. This doesn’t align with the idea that bees are brilliant navigators who can accurately find their way home. If we consider bees in a theoretical ‘natural state’ (like in the Arnot Forest) their colonies are in trees at a very low density; the nearest neighbour will be hundreds of metres away, or further. They do not need pin point navigational accuracy. Once they get within ten metres of home they just need to hop into the tree with bees in it. There aren’t lots of trees with bees in them, all bunched together a few feet apart.

When I visited Randy Oliver in California four years ago he was running a field trial on drifting workers. He was tracking workers from hives that were collapsing due to varroa overload, with workers in healthy hives as a control. Workers from both diseased and healthy hives drifted, some up to about a mile away. We can theorise about diseased workers leaving to save their colonies, or perhaps going to rivals to spread their sickness and knock out the competition, but what about the drifters from healthy hives?

Mating Success Is Variable

If we keep healthy hives the drifting issue is not really a major concern. However, when it comes to virgin queens on mating flights, it’s a matter of life and death. Be honest, if you raise a reasonable number of queens each season, what percentage get successfully mated? It varies from place to place, year to year, month to month, but it’s not anything like 100% is it? Sometimes the mating nuc will have queen cells, or a virgin, which means that they rejected the cell that we gave them and decided to make their own (or she just didn’t go on mating flights). However, sometimes there is just no queen, and no cells either. She may have returned to the wrong nuc or (rarely) been eaten by a bird.

I recently spoke to Mike Palmer about mating success in mini mating nucs. He had his arranged in blocks of four, each entrance perpendicular to it neighbour. This ‘four way’ arrangement was what Brother Adam used on his mating hives on Dartmoor. Mike’s production line of queens relies on mating success of about 65%, but he was finding that it was dropping below that. He decided to try arranging mating nucs in pairs (two way) with entrances pointing in opposite directions, with each pair as widely spaced apart as possible. His nucs are also painted with distinctive colours and shapes so that each looks different. This resulted in several ‘takes’ of over 80%, and it lines up with the improved mating success that Paul Horton found by using coloured correx landing boards on hives. Nature isn’t so simple, though, and Mike also had a terrible take with his two-way nucs and an amazingly good one with four-ways.

Navigation and Visual Cues

You’ll notice a distinct lack of references to scientific papers in this article. I did have a little root about into the navigation issue, and was sent something on how bees can learn and unlearn certain visual cues. Regarding navigation, there was this research and this which suggests a mechanism that bees may use to find their way home using ‘optic flow’. It’s all a bit over my head, but this mechanism would benefit from landmarks or variations in the environment. Research tracking bees has shown that they do use landmarks to help with navigation. However, once the bees get into an apiary they have to select their particular hive entrance rather than a neighbour’s. Karl von Frisch showed that they can see colour (not red) and did some work on pattern recognition. One paper seems to contradict a lot of others; it concludes that, “The trained bees did not learn shape in general; they learned to discriminate by detecting and learning the position of one or more simple cues. There are only a few of these cues and they are used over and over again.”

Blind Love?

With queens on mating flights, there is also research showing that the presence of semen in her spermatheca can trigger a deterioration in her eyesight. The evolutionary logic is that the semen of successful drones has the effect of reducing the chances of queens taking additional mating flights to receive sperm from rival drones, because she can’t see properly. Sounds crazy, but nature is a weird and wonderful thing. Then, of course, there is evidence that certain insecticides, such as neonicotinoids, can mess with the ability of honey bees to navigate effectively.

Vexed though I am, my general feeling about all of this is that putting hives close together in apiaries causes an increase in drifting and lost queens on mating flights. I am going to try to keep hives further apart, pointing different ways, and use colours and markings on landing boards. I also wonder if, even though bees are pretty good at finding their way home, they are not unduly concerned about joining other colonies in the area, and that this happens quite a lot.