bee biology

The Spectrum of Bee Sociality

When we think of bees, we usually think of social creatures. We often see drawings of bees circling a bulbous nest dangling from a tree. The bees look down at us and scowl or smile, depending on the artist’s worldview.

This article first appeared in American Bee Journal, Volume 161 No. 12, December 2021, pp. 1297-1301.

In truth, bees have an enormous range of social behaviors. The eusocial (meaning truly social) species like honey bees cap one end of the spectrum, while solitary bees such as orchard mason bees mark the other. But between the two extremes lies a fascinating amalgam of alternative lifestyles, each with pros and cons.

Honey bee aficionados sometimes try to convince us that eusociality is the ultimate goal, the pinnacle that other bees covet. But the record of natural history does not support that view. In fact, the fossil record shows that some species moved toward sociality before reversing course, evolving back toward a solitary lifestyle.1 When you realize that both solitary and eusocial species have endured for eons, it’s hard to say that one is better than the other. Both seem to work just fine.

Eusocial insects are everywhere

All seven species of Apis are eusocial, but they are certainly not the only bees — or the only insects — that live that way. Bumble bees, all of them, are eusocial, as are the stingless bees. In addition, we have eusocial wasps of various types, including those that live in the globose paper abodes.

I’m the unwitting owner of a ginormous paper abode at this very moment. It hangs in the upper branches of a cedar tree and spews bald-faced hornets, Dolichovespula maculata, which feed on my equally eusocial honey bees. I spent all summer looking for the nest, only to discover it right above my head as I walk out the front door.

Beneath my house lives a colony of highly eusocial ants. They bloom every August and crawl up the siding of my house in waves that make me itch. After I spray them to ground with a garden hose, they disappear for another year.

In spring, teeming hordes of red-and-black fire ants appear at the top of the hill behind my house. They ever-so-socially writhe over one another as they shape piles of fir needles into two-foot pyramids that pulsate with formic acid.

Luckily, I don’t have termites. Those pests, pleasantly known as social cockroaches, are not even in the order Hymenoptera, but they managed to evolve a social structure similar to that of bees, ants, and wasps. So you see? Eusocial insects are ubiquitous.

Mason bees are strictly solitary. Even though they often live very near to each other, each nest is separate from all others without any cooperation between females.
Mason bees are strictly solitary. Even though they often live very near to each other, each nest is separate from all others without any cooperation between females. (All photos by Rusty Burlew except as noted)

Pros and cons of the eusocial life

Some advantages of the eusocial life are obvious, such as defense. The idea of getting stung by many bees is more off-putting than being stung by one, a thought that keeps intruders wary. The same holds for fire ants. If you’ve ever stepped on a fire-ant hill and had them run up your legs, you know the feeling of terror.

Not only are the numbers intimidating, but a large group of individuals can keep many eyes on a developing situation. See that skunk coming toward us? Prepare to pounce!

Cooperative food and water acquisition is another benefit. When many individuals are hunting for supplies, finding the things they need is more likely. A group can certainly cover more ground than a single bee, and the group can collect it more efficiently. On the other hand, the colony needs more supplies as the group gets bigger, and there is more to lose should it fail.

Highly eusocial insects are more likely to overwinter, so cooperative warming of the brood nest becomes important. Solitary bees do not keep each other warm, but neither do they have the need. Most solitary bees hibernate as either pupae or adults until the weather warms in spring.

Density itself engenders problems. Large colonies are easily visible and make excellent targets for hungry animals like bears. Competition for food within a colony can be intense, too, and if food becomes short in the winter, the entire colony can perish. And as beekeepers know, disease and parasite transmission among colony members is treacherously efficient.

The spectrum of sociality

If you look at sociality as a continuum, you will find a wide range of variations that fall between the extremes of solitary and eusocial. I’m fond of saying that honey bees are outliers in the bee world, and this is especially true of sociality. Honey bees are at the very pinnacle of cooperative living, but that doesn’t mean other bees are inferior, only different.

Solitary bees

At the “simple” end of the spectrum, you will find the solitary bees. However, when you examine the day-to-day existence of these bees, you will find their lives anything but simple.

A solitary female is truly the full-meal deal. Except for a brief tryst with an impatient male, she performs every step of the child-rearing process by herself with no help from parents, siblings, neighbors, in-laws, or men. She is the home builder, egg layer, provisioner, security guard, and maintenance staff. A solitary bee mom works her entire life without ever seeing results. She’s born alone, works alone, dies alone, and never even meets the kids. Now that’s rough.

Who are these intrepid bees who work so hard and ask so little? Most of them. Most bee species are solitary, and everything else is an exception. The following list details some of the major types of sociality, but note that all bees do not agree on the details and neither do all melittologists. The definitions of social types are as fluid as the bees within. In the descriptions below, I’ve adapted the groups proposed by O’Toole & Raw in their 2004 book, “Bees of the World.”2

A clue to solitary vs. social living is the size of the queen’s eggs. Honey bee eggs are minute, about 1.2-1.8 mm long, but a queen can lay up to 2000 per day. Carpenter bee eggs can be over 15 mm long, but the solitary carpenter may lay only 8 to 10 in her lifetime. (Public domain photo)
A clue to solitary vs. social living is the size of the queen’s eggs. Honey bee eggs are minute, about 1.2-1.8 mm long, but a queen can lay up to 2000 per day. Carpenter bee eggs can be over 15 mm long, but the solitary carpenter may lay only 8 to 10 in her lifetime. (Public domain photo)

Communal bees

The first step up from a purely solitary existence is communal living. I think of these bees as the condo dwellers. The members of the condo association have a common entrance — the front door — and a vestibule of sorts that leads to individual units. Once inside, each female maintains her own unit, separate from everyone else. She excavates and maintains her own brood cells, and collects provisions for her offspring. Except for that common entrance, she is like any other solitary bee, building, and provisioning until she dies, without ever meeting her spawn.

Forty or fifty females may share the common area, barely nodding to one another as they come and go. But so much activity at the front door is a safety feature. The entrance is rarely unguarded as bees come and go, and someone is usually on hand to wrestle an intruder. They have a built-in neighborhood watch.3

Communal living is not mandatory for most of the bees in this group. In species where communal living is common, some individuals will inevitably choose the solitary life. So just across the street from the condo, you may find single-family homes.

Researchers believe communal arrangements begin when several sisters emerge inside a single-family nest and decide to expand the nest rather than go out and find new ones. This is thought to be the safer option for both the individuals and the species.

Quasisocial bees

Yet another arrangement is called quasisocial. Quasisocial living occurs when several bees in a nest emerge at the same time. There is no “mother” in attendance because she is long gone, having laid her eggs, provisioned them with food, and left. For a time, these young females — who are sisters or half-sisters — continue to share the natal nest, much like the communal bees.

However, instead of each bee minding her own business, one female will dominate and take over the nest. She will redecorate, repair any damaged brood cells, and build new ones. Then she will lay eggs.

For a while, the sister bees will help with the renovations, foraging, and provisioning. The period of cooperative homemaking is the quasisocial period. It is usually quite short and, after a few days, the once-helpful sisters go out and find nests of their own.

Because this type of social arrangement is temporary, it’s difficult to define and hard to detect. Like a communal nest, it is dynamic, changing with the whim of the occupants. In contrast to eusociality, where a bee’s entire existence depends on a group, transitory sociality gives a bee freedom to choose. She can hang with the crowd or go out on her own.

Temporary sociality may be nature’s way of assuring that at least one nest gets off to a solid start. The later nests — which require site selection and digging a nest from scratch — are more of a gamble and less likely to succeed.

Semisocial bees

In semisocial bees, we see the first hints of a division of labor. Nest mates, who are also sisters, are divided into egg layers and foragers. The layers and foragers work together to raise the brood. However, these bees can change roles at any time, allowing the colonies to become quasisocial. Like any other quasisocial group, most of the females may eventually leave and start nests of their own.

O’Toole and Raw group these first three levels of social behavior (communal, quasisocial, and semisocial) into a larger group called parasocial. The parasocial colonies are similar to one another because they all begin with sisters or half-sisters in the natal nest where they overwintered. Some will stay with that nest, at least for a while, and the rest will leave to fend for themselves.

 Bumble bees are primitively eusocial bees. Unlike honey bees and stingless bees, the colony does not persist throughout the year. Instead, the mated female goes through a period of solitary living lasting throughout the winter and into spring. Colony life begins after her first batch of brood emerges.
Bumble bees are primitively eusocial bees. Unlike honey bees and stingless bees, the colony does not persist throughout the year. Instead, the mated female goes through a period of solitary living lasting throughout the winter and into spring. Colony life begins after her first batch of brood emerges.

Subsocial bees

In a subsocial species (yes, all the names sound alike), the female foundress raises her brood into adulthood, feeding, protecting, and providing for them until they are fully functioning adults. But instead of hanging around the home front and assisting mom with the chores, each newly emerged female goes out into the world and builds a nest of her own.

This lifestyle earns them a position closer to the eusocial bees because — at least for a time — more than one generation inhabits a nest, giving mom a chance to meet her offspring. The Allodapini, a tribe of small carpenter bees common in Australia, contains many subsocial species.4

Primitively eusocial bees

Eusociality comes in two types, colonies that are primitively eusocial (bumble bees and some sweat bees) and those that are highly eusocial (honey bees and stingless bees).

The major difference between the two groups is that primitively eusocial bees go through a period when the founder queen is solitary. Later in the year, following the eusocial period, the colony reverts to subsociality, meaning new females go out on their own rather than staying at home.

Bumble bees: When a mated bumble bee gyne emerges in the spring, she is solitary. She raises her first batch of brood by herself, just like any other solitary bee. However, after the first brood emerges, the sexually immature daughters assume the care and feeding of subsequent batches of brood. At that point, the former gyne restricts herself to egg-laying and becomes queen of the colony.

The colony remains in the eusocial mode throughout the rest of the season until fall when the queen produces reproductives — drones and gynes. Instead of staying in the colony and helping the queen, the gynes mate and look for a place to overwinter. At this point, the colony becomes subsocial. New bees leave the nest rather than helping to maintain it, so the colony begins to fail and, eventually, the queen will die.

Sweat bees: Sweat bees have a wide range of sociality types, depending on the species, but the primitively eusocial ones share some traits with bumble bees.

Most notably, the reproductives — males and virgin females — emerge late in the season and mate. This means the females do not need to find a mate first thing in the spring. As soon as they emerge from hibernation, they can begin a nest.

Like a bumble bee queen, the primitively eusocial sweat bee begins life in a solitary state. She builds a nest, provisions it, and raises a batch of sexually immature females who take care of the nest and rear their sisters. At this point, the colony is eusocial, and it maintains itself until the fall reproductives are produced. The females mate, hibernate, and become the solitary foundresses for the next year.

All the species have slight differences, however. In some species, the first batch of brood may contain reproductives, some of which will mate and found new colonies right away. This behavior is subsocial, while the rest of the colony moves on to embrace eusocial behavior until the end of the season.

This is a small aggregation in compact gravel. The bees living here are Halictus sweat bees. From the surface, you can’t tell if the bees are solitary or parasocial.
This is a small aggregation in compact gravel. The bees living here are Halictus sweat bees. From the surface, you can’t tell if the bees are solitary or parasocial.

Highly eusocial bees

So what makes something highly eusocial? According to an article on Nature.com, a society of animals must meet four criteria to be called highly eusocial.5

  1. Members must live in a group that shares a nest
  2. The group must contain overlapping generations
  3. The group must have a reproductive division of labor, meaning there are reproductive members and non-reproductive members
  4. The members must practice cooperative brood rearing, meaning some members raise other members’ kids

As you can see, this definition fits the honey bee colony to a tee. But what makes honey bees so fascinating is not these four items, but the system of communication they developed to become efficient at the things the colony needs to do. In my mind, communication among the membership — and the ability to collectively solve problems — is the thing that sets them apart.

Aggregate living

An entirely distinct living arrangement, one not found on the sociality spectrum, is an aggregation. Aggregations are simply groups of nests found close together where there is no social interaction between neighbors, not even a common entrance. Aggregations can be small, containing just a few bees, or they can be huge, with hundreds or even thousands of individual nests. Think of these as single-family housing developments.

Bees live in aggregations built on flat land, embankments, and sand dunes. Tube-nesters like mason bees and leafcutter bees may live in bundles of reeds or bamboo stems — close together but completely separate from one another.

In other cases, some nests within an aggregation may fall into one of the social categories. For example, in the midst of many solitary bee nests may be a few that are communal or quasisocial. These aggregations are similar to mixed-residential zoning — one aggregation contains both single-family and multifamily residences. From the outside, the entrances all look the same, so you can’t tell what lies beneath without surveillance to monitor who comes and who goes.

This Halictus bee is just starting to dig a new tunnel. The dirt flies out behind her as she aggressively removes the soil.
This Halictus bee is just starting to dig a new tunnel. The dirt flies out behind her as she aggressively removes the soil.

The origins of aggregates

Melittologists are not sure why aggregations occur. It’s possible that excellent nesting sites are so scarce that when one is found, everyone squeezes in. Just like humans. Another theory suggests that since solitary bees can’t travel far, they take the first available location they find after leaving the natal nest. Others think it’s related to the availability of forage or nesting materials.

Bees in aggregations don’t even need to like each other. I’ve found aggregations containing multiple species at the same time, big holes and little holes all intermingled — bees flying every which way with cleptoparasitic bees circling the perimeter.

If you are lucky enough to find a large aggregation, pull up a lawn chair and enjoy. A busy aggregation is reminiscent of a cityscape filled with commotion. You will see squabbles at nest entrances when a returning bee mistakenly enters the wrong one. You will see fights, collapsed front doors that require a rebuild, and pebbles that rock but won’t move. And you will see kleptoparasites trying to break and enter and predators like bee flies, robber flies, and wasps looking for a meal. Even birds and lizards take advantage of the mayhem, and columns of ants collect the carnage.

Which type are you?

Since this magazine caters to beekeepers, I imagine that most of you favor highly eusocial insect colonies over the rest. Certainly, if you equate “complex” with “superior,” highly eusocial would win. On the other hand, all these other systems have persisted generation after generation, a sure sign that they work and deserve a continued place in our complex world.

But what about you? If you like to travel light, change plans on a dime, and spend time alone with books, the eusocial life is probably not for you. If you like loud parties, multigenerational retreats, family reunions, and enormous weddings, the solitary life may not appeal.

Bees remind me that life offers something for everyone. Instead of comparing, contrasting, and scoring the various lifestyles, perhaps we should just accept all the species and the things they do for us. In the end, perhaps we should just let them bee.

Rusty
Honey Bee Suite

This Sphecodes bee is a kleptoparasite of the Halictus in the aggregation. They fly low over the aggregation or wait patiently on the sidelines. When a female Halictus leaves her nest, the Sphecodes swoops in to lay an egg on the pollen provision.
This Sphecodes bee is a kleptoparasite of the Halictus in the aggregation. They fly low over the aggregation or wait patiently on the sidelines. When a female Halictus leaves her nest, the Sphecodes swoops in to lay an egg on the pollen provision.

References

  1. Michener CD. The Bees of the World, 2nd Ed. Johns Hopkins University Press. Baltimore.
  2. O’Toole C and Raw A. 2004. Bees of the World. New York, NY: Facts on File, Inc.
  3. Melittologists disagree about how much protection communal living confers. Although more members mean more surveillance, more members also create a more visible target.
  4. Houston T. 2018. A Guide to Native Bee of Australia. Victoria, Australia: CSIRO Publishing.
  5. Plowes N. (2010) An Introduction to Eusociality. Nature Education Knowledge 3(10):7.
News from the Field
According to an article in The Guardian, new research published in Proceedings in the Royal Society B, shows that climate change may favor small-bodied bees. Large bees, such as bumble bees, have difficulty shedding extra heat, while smaller species seem to handle it better. The researchers also reported that ground-nesting bees seem to fare better than cavity nesters because the ground stays cooler than the air.

6 Comments

  • Always fascinating reading your blogs and the change in writing styles this time from your opening to the more technical aspects further in was great [ok maybe it was just me]. Question about one component in the early part of the blog. “In spring, teeming hordes of red-and-black fire ants appear at the top of the hill behind my house. They ever-so-socially writhe over one another as they shape piles of fir needles into two-foot pyramids that pulsate with formic acid.” We live very close to each other and I never thought of the red and black mound-building ants as fire ants but I am certainly not an entomologist. They certainly don’t seem to fit the bill I have dealt with in Mississippi. Are our local variety a subspecies of sorts? As long as they aren’t in our pastures or apiary we’ve always just let them do what they will do and actually enjoy watching their growth year to year.

    • Hey Gary,

      Thanks for the compliment! Much appreciated.

      It’s funny, but I’m in the middle of writing an article about scientific names, which most people dislike. But your question is a perfect illustration of why they are important. Our so-called fire ants are a different species than what you have down south, different genus, too. Common names are like that: You’ve got an ant that bites and then spits formic acid into the wound? Well, that’s a fire ant, even though there are lots of different kinds. What we have here is Formica obscuripes, the western thatching ant. What you had in Mississippi was probably the red imported fire ant (Solenopsis invicta) or maybe the black imported fire ant (Solenopsis richteri). From what I’ve read all three bite (and spit) about the same.

      I should have been more specific, but I was only trying to illustrate the presence of social insects, so I left our the details. My bad.

  • Thank you Rusty for a very interesting and informative article. I wonder how many people have thought only about the functions of pollination and honey production. Honey bees obviously perform both of these. While honey bees are the chief producers of honey, they are not alone when it comes to pollination.
    I would enjoy learning more about how we can identify and assist other pollinators which are native to our particular locations. This would be of special interest with regard to the various food crops which we need for human and farm animal nutrition.

    • Wilfred,

      Bees and other pollinators are difficult to identify once you get past the most common ones, but it sure is fun to learn.

  • Hey there! Love all of your informative posts. I myself am very passionate about bees, though living in the city I don’t have the possibility of taking care of them here. But I do enjoy reading about all things bee-related and I try to donate to/support associations that help the bees. I usually also keep an eye out for anything else that tries to raise awareness about bees etc Recently I stumbled onto a video game called Bee The Best. A fun party game that aims to make people think more of bees! It’s exciting to see people give them the attention they deserve.

  • I’m testing posting here. I’m gonna share an insane story but it’s true. I’m an ex-radio tower hand, twenty years. I then settled down and my neighbor attacked me with a microwave magnetron to try and get me to sell my land. I caught him 16 years later. He killed 30 people with heart attacks, strokes, and cancer up to six miles away and did not know it, including his mother and daughter. He tried beekeeping and failed at it. The reason he failed was because my house was covered in barn tin. It reflected the microwave back at him and his homestead. Come to find out bees get aids also. The microwave was lowering their immunity. Then years later I met a man who had bees under his house. It was in a low spot and shielded from radio towers; it was a dead zone. The bees would not leave. They had escaped from his neighbors’ yard right after a three g tower had been built.

    The moral of the story, shield your hives from radio towers and you will have healthier bees. I just started my first hive and I have it on the opposite side of my house from a radio tower. They seem very healthy and active.

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