Communal nesting bees: Agapostemon

Agapostemon virescens female on Echinacea purpurea

The insect order Hymenoptera (including ants, bees, and wasps) used to be considered the model of nonhuman sociality.  The famous ecologist (and one of my personal academic crushes) E.O. Wilson used ants as a model for understanding how sociality evolves.  In a talk he recently gave at my uni, he explained that understanding sociality in other organisms is the first step toward understanding it in ourselves, which then allows us to approach the questions: why are we here? where did we come from? where are we going?

Agapostemon bees are sooooo shiny

But sociality, like all things, exists on a gradient.  From what we consider to be “true sociality” (or eusociality) all the way to solitary, with everything in between.  Scientists have struggled to provide precise definitions of each level of sociality, but exceptions and strange things inevitably confound attempts to do so comprehensively.

diving for nectar

In my opinion, bees are a great system for studying sociality because they exist at all of these different levels.  There are solitary bees and eusocial bees, communal and semisocial bees, bees that form dense aggregations and bees that lay a single egg inside a single nest cell in the pith of a reed.

Agapostemon virescens, in flight

I should state that I am biased toward bees.  I love them and although that hurts my impartiality as a scientist, there it is.  I am but human.

How can you not love this face?

Without exhaustively addressing the different stages of sociality and the respective phylogenetics of such, I would like to present to you a communal genus of bee: Agapostemon.

What’s this among the grass?

This genus is North American in distribution, and it is especially notable for its beauty: iridescent green thoraxes, often with yellow and black bands on the abdomen.  Sometimes the females are iridescent all over.

A closer investigation.

Agapostemon species are communal because each nest is solitary but the nests exist in aggregations.  Bee scientist Laurence Packer says, “Semisocial is a reproductive division of labour among individuals of the same generation, communal is nest sharing with each individual acting as if solitary within the nest – i.e. digging, provisioning and ovipositing in their own brood cells.

Hello? Anybody home?

Of course, how much interference and cheating there may be in such “communal” nests is largely unknown.  Though reports of fights at nest entrances, rather than welcoming “with open arms” (or more accurately open mouthparts to permit food exchange as is known for Australian communal bees – Kukuk papers), have been made but not, to my knowledge, studied in any detail.”

I see you, little bee!

My friend found these nests in his yard.  There are four entrances, so there is an aggregation, but a different bee guards each nest, so they are communal, not semisocial.

“Go away, silly human!”

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20 thoughts on “Communal nesting bees: Agapostemon

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      • Just wondering because I’m sitting on a few sweat bee photos until I can identify them. I’m sure it’s an Agapostemon species, but not sure which.

      • Ok so I looked back through these photos…in general sericeus has a lot more yellow on it than virescens, especially in the legs (the hind tarsus should be mostly yellow in sericeus), but I think I was being careless in identifying the photos and the pollen on the first male’s legs might have triggered as yellow. Without seeing his legs better he’ll just have to be Agapostemon sp. The second one I am pretty sure is virescens, you can get a good look at the legs and see how dark they are, plus the stripes on the abdomen look white, which seems to be more of a virescens trait. As with any photo based ID, though, take it with a grain of salt. Does that help? Want me to look at your photo?

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