There you are, stood by your hive, trying to see if you’ve done your hat up properly and whether the smoker’s still alight and what might be happening at or around the entrance and whether it’s worrying or reassuring or both, going through the mental checklist of all the equipment you haven’t got ready that you’ll need to deal with whatever you’re hoping the bees almost certainly shouldn’t have done, and painfully wondering if the trouser pocket is really the best place for a Baldock cage while, with a muted thunk, a bee lands flat on its back on the top of the hive, waving her legs in the air as if angling for a tickle.
You might, once in a while, wonder why. But, more often than not, you’re going to have fifty thousand other things to worry about and by the time the lid is on the floor, and you’re busy looking for five things at once while remembering not to trip over the smoker, it has become a vague and unreliable memory.
Occasionally people ask. And the standard answer is that returning foragers, heavily laden with honey, will often misjudge their final approach.
For various reasons, this doesn’t ring quite true. One reason is that bees have evolved over a very long time to do what they do quite well, and being able to land while carrying nectar is a vital part of that. Analysis of bee landings shows they have a clear set of mechanisms, depending on the angle of surface they’re landing on, involving a brief period of hovering (1/5 of a second or less), which suggests the landing process is much more than a free-style dive*. And secondly, it’s a very small proportion of returning foragers that seem to land upside-down at any one time, which suggests it’s not a general problem caused by, say, the size of the payload or the direction of the wind.
So here are some possibilities that have been suggested:
- Old age – Foragers have a finite lifespan and a forager on her last legs may lose her faculties gradually, making accurate landings near the end of life more difficult.
- Low fuel – Lack of food reserves may mean the bee has too little energy to complete the landing process properly.
- Physical damage – Damage, especially, to hind legs or wings would mess up the landing process.
- Confusion – Bees navigate using the sun as a marker and do so, even when its cloudy, because sunlight is ‘polarised’, and the bee is able to measure that polarisation. Secondly, we know that reflected light, even when scattered from a dull metal surface, keeps its polarisation. And, finally, we know that the ocelli (the three simple eyes on top of a bee’s head) are involved in working out which way up a bee is, and seem to be able to detect polarisation**. It may be possible that, at a specific angle, the light reflected from the metal of a hive roof interferes with the polarisation information from the sun, and gives a bee approaching at that precise angle, the sensation of being upside down, which the bee then corrects.
- Varroa – A bee harbouring varroa mites beneath its segments may be prompted to land heavily, and upside down, in an attempt to dislodge them.
- Collision – hitting another bee on approaching the hive might knock one of them onto the roof.
- Pesticides – Some combinations of some substances seem to disrupt effective foraging by affecting the bees’ ability to navigate. Perhaps something similar is causing landing problems.
As far as I can tell, nobody has yet studied this phenomenon, so nobody knows if any, all or none of these possibilities is correct. That’s understandable because there are several possibilities, which makes it difficult to study without spending a lot of time, effort and probably money that might be better spent elsewhere.
And that’s why there are still many things about bees that we may never know the answer to, many of which we may have seen with our own eyes. Things we might call obvious, but which are also mysteries. They may spark our idle curiosity, but until idle curiosity can line the pockets of grant-hungry scientists, that’s as far as it will go.
In some ways, it’s similar to the neonicotinoid issue, in which governments and scientists seemed to take a very long time to react to an apparently obvious problem. One reason it took a long time was because while there wasn’t a proven significant effect, there wasn’t a proven reason for looking for one.
Happily, science is not exclusive, and many dedicated amateurs have made valuable contributions to science. So this may be your opportunity – if you’ve the time and the inclination, pick a possibility you fancy, design your experiment and carry it out. It really is as simple as that.
*Evangelista, C., Kraft, P., Dacke, M., Reinhard, J. and Srinivasan, M. V. (2010). The moment before touchdown: landing manoeuvres of the honeybee Apis mellifera. J. Exp. Biol. 213, 262‑270.
**Ribi W1, Warrant E, Zeil J. (2011) The organization of honeybee ocelli: Regional specializations and rhabdom arrangements. Arthropod Struct Dev. 40(6):509-20