Eventually everything in nature starts thinking about reproduction. It’s what we do, and each species exhibits specific signs when they have reached sexual maturity. Humans get hair and breast tissue. Bower birds make elaborate nests. These are obvious outward signs, but what piece of neurobiology triggers the first steps of a reproductive cycle? Honeybees…how exactly do bees know it is time to split a colony and reproduce?
I am not referring to an individual queen and her virgin flight. That’s programmed. But swarming to produce a new colony, that is a hive decision made by the workers. Beekeepers know of several reasons why bees swarm, but knowledge of the precise trigger mechanisms were hazy. Scientists at Cornell university decided to take a look and found that it depends on size. If a colony reaches 4,000 bees then worker bees stop exclusively making hexagonal cells for worker eggs, and start making the slightly larger drone cells too.
Drones are the men, the haploid product of eggs laid by the queen whose sole purpose is to mate with a virgin queen and in Darwinian fashion, pass on their genetics from this successful hive. A queen can find a drone congregation area and mate with up to 12 drones from various hives in her quaintly-termed nuptial flight (though to a human that would count as an orgy, but hey, she usually only gets to do this once in her life. Don’t judge.) After coming home all stocked for life with sperm a new queen may find the old queen has swarmed and she has the old hive, or vice versa (though more rarely). And voila, 2 hives where there once was but one.
Obviously there are way more steps happening back at the hive to produce a swarm, and just because there are men does not mean swarming in that hive is inevitable, but it all starts with the drone cells and the magic 4,000. Call it the initial investment.
We have proven that bees can count, at least to 3 (see below reference). But 4,000? How does an individual worker bee ‘knows’ how many other workers there are in its colony, and how does a number translate into building a cell that is usually over 1.1 mm larger in diameter than the average worker honeycomb diameter (4.6-5.1 mm)? The Cornell team speculate that this might have to do with how crowded individuals feel while working side-by-side in the hive, which may also have a pheremonal component.
This is the article I read. It refers to the original paper in the journal (Naturwissenschaften – The Science of Nature)
Smith, M. L. et al. (2014). A critical number of workers in a honey bee colony triggers investment in reproduction. Naturwissenschaften – The Science of Nature. DOI 10.1007/s00114-014-1215-x
This is that article, but I cannot find it on the web.
As for numerate bees, here is the study abstract online: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004263