Anti-social beehaviour
After honey-making and their ability to sting, bees are probably most well known for their sociality. Except these traits aren’t as common, or exclusive, as one might think.
The honey we eat is only made by honey bees (about eight out of the 20,000 or so bee species), but it’s also made in much smaller quantities by stingless bees, bumble bees, and some species of ant and wasp.
As for stinging, it’s only female bees that can sting, and there’s a whole family of bees – the aforementioned and aptly named stingless bees – that can’t sting at all.
And while we’re all familiar with honey bees’ large, highly organised hives, about 90% of bee species are solitary, typically nesting in small subterranean burrows or inside twigs, rather than living communally.
The sort of complex social behaviour that honey bees, as well as ants and termites, engage in is known as “eusociality”. This is the highest level of social organisation we recognise in animals. It’s defined by a population having overlapping adult generations, cooperative care of young and division of labour (usually creating a sort of biological caste system).
Compared to solitary bees, eusocial bees have many more genes involved in smell, specifically the molecular receptors that recognise chemical pheromones, so they can distinguish strangers from nest mates, detect different social castes and communicate effectively.
However, one family of eusocial bees – the halictid, or “sweat”, bees – can adopt either lifestyle, living alone or as part of a colony.
This is interesting for two reasons. First, systems in which closely related species or populations differ in their social organisation are extremely rare. Second, this social-solitary flexibility is fertile ground for studying the beginnings and evolution of complex social behaviour – not just in bees, but humans too.
For some sweat bees, this lifestyle choice seems to be very plastic. The orange-legged furrow bee (Halictus rubicundus), for instance, can have solitary and eusocial colonies appear simultaneously in the same population, flipping back and forth depending on the climate.
But for another sweat bee, Lasioglossum albipes, sociality is decided by genetics. Researchers found that one gene, syntaxin 1a, that regulated the release of neurotransmitters was about 15 times more active in social bees compared to solitary ones.
And it’s not just bees. For example, locusts that feed on their own but then migrate together have increased syntaxin activity during migration. Mice lacking syntaxin have altered levels of hormones that influence social behaviour. And several studies in humans have implicated syntaxin in autism and other hyper- or hyposocial behavioural disorders.
Altered activity in a similar set of genes, also associated with autism in humans, was also found to make some honey bees anti-social. Where honey bees instinctively care for immature queen larvae and attack nest intruders, the affected individuals failed to respond to these stimuli at all. And yet the other bees didn’t seem to mind having them around.
So even though bees and we are very different, it suggests that there are similar genetic “toolkits” that have shaped the evolution and variation of social behaviour across both insects and mammals.