Sweet dreams: sleeping clusters in bees

As you already know, I love bees. And what could be cuter than a sleeping bee? (Not much, as it turns out.) I often find little sleeping bees inside curled up petals, on the underside of thistle flower heads, or with their faces buried in flowers (I guess so that they can wake up to a sweet treat!). But in Australia, I was treated to a cluster of sleeping bees:

Lipotriches (or Austronomia?) aggregating for the night in a grassy meadow

Male Lipotriches (or maybe Austronomia? I can’t tell if these two genera are synonymous) aggregating for the night in a grassy meadow

I found this big stag party on an outing with the illustrious photography, Mark Berkery.  This is what is known as a sleeping aggregation (or sleeping cluster) of male bees.  (Also, if you’re into adorable bees, check out this short, cute video.  It just calls them “worker bees”, but they are actually males aggregating for the night.) Here is a description from “The Social Behavior of the Bees: A Comparative Study”, by Charles Michener:

“They consist of groups of males, rarely with a few females, which assemble in certain places to pass the night. There may be up to two or three hundred bees involved, usually with one species but occasionally mixed…The clusters are commonly on exposed stems, the bees clinging with their legs, often also with their mandibles.  Some species also adopt a bizarre position, projecting rigidly at right angles from the twig or stem which they grasp only from the mandibles.”

At the end of a dead stem

At the end of a dead stem

But nobody knows why the males aggregate at night.  There is some notion of a “predator dilution effect”, such that a predator must choose to feed on only one of the many available bees.  But this kind of group selection argument is a hard sell among many ecologists.

Perhaps the most convincing explanation of this kind of behavior is the encounter dilution effect, proposed by Turner and Pitcher (1986).  Here’s a clip from Wikipedia:

“In the detection component of the theory, it was suggested that potential prey might benefit by living together since a predator is less likely to chance upon a single group than a scattered distribution. In the attack component, it was thought that an attacking predator is less likely to eat a particular animal when a greater number of individuals are present. In sum, an individual has an advantage if it is in the larger of two groups, assuming that the probability of detection and attack does not increase disproportionately with the size of the group.”

The other beautiful sleeping bees that we found in the meadow were these Amegilla (here’s another cute article on them):

Aw, don't be shy little guy

Aw, don’t be shy little guy

So we’re heading into winter in the northern hemisphere, but if you’re Australian, check out your meadows just before dusk!  See if you can’t find some sleeping bees.

Bye bye now!

Bye bye now!

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18 thoughts on “Sweet dreams: sleeping clusters in bees

  1. I see sleeping bees but I have never seen a group, that must be something to see. I love the Amegilla. It reminded me of my Anthophora albigena that love my sage in the garden in the summer, so I checked it out and they are related in the Anthophorini.

      • I get other Anthophora here but this is the only one so far with green eyes but they are all pretty cute. Anything called a Hairy-footed flower bee must have been lovingly named. Plumipes is one of the few solitary bees to have a common name in English, if you put the bumbles to one side.

      • I agree, most of the solitary bees are nameless…it makes outreach a bit hard. “Oh, what is this shiny green one?” “It’s a sweat bee.” “What about this little black one?” “Uh…that’s also a sweat bee.”

        But the Amegilla featured here does also have a common name, the Blue-banded bee. There is another Australian Amegilla called the Teddy Bear Bee!

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