- vast majority are solitary, inc. (1) burrowing or mining bee; (2) mason bee; (3) leaf-cutter bee; and (4) carder bee. 
  - Carpenter bees are traditionally considered solitary bees, though some species have simple social nests in which mothers and daughters may cohabit. However, even solitary species tend to be gregarious, and often several will nest near each other. It has been occasionally reported that when females cohabit, there may be a division of labor between them, where one female may spend most of her time as a guard within the nest, motionless and near the entrance, while another female spends most of her time foraging for provisions.   wiki
  - Although most bees are solitary or subsocial, the family Apidae contains three distinct groups that exhibit eusocial (highly social) behavior:  these are commonly known as stingless bees, bumble bees, and honey bees.  src
  - In the book "Bees of the World" (1991) by Christpher O'Toole & Anthony Raw. ISBN: 0816019924, bumble bees (Bombus) are not highly social bee like those 2.  They are, with the sweat bees (Halictidae), classified as primitively eusocial bees because their colonies pass through solitary and subsocial phases.  A primitively eusocial colony is always founded by a single, mated female, and thus passes through early solitary and subsocial phases.  In contrast, stingless bees and honey bees form permanently social colonies.  In their colonies, there is a clear distinction between a single queen and hundreds or thousands of sterile workers.  The queen is totally dependent on the workers for her food, and new colonies are organized by the workers.

  -  Terminology : I think using primitively social & highly social is better than primitively eusocial & eusocial.

  - (cont.) Some species of sweat bees (Halictidae) are solitary, while others exhibit varying degrees of social behavior.  Every nest is founded by a lone female.  In the social species, the daughters remain with the natal nest, construct new cells and forage for food.  Female sweat bees mate before hibernating for the winter.  They do not have to mate before founding a nest in the following spring.  They raise a first generation that consists entirely of daughters.  These cannot mate and are 'predisposed' to remain with their natal nest and act as non-reproductive workers.  In a sense, therefore, by producing no males among the first generation, a female manipulates the behavior of her daughters in such a way as to make it likely that they will remain to help rear later generations.  In the northern hemisphere, most halictid colonies produce males only in the last generation of offspring, in late summer and early autumn.  
  - (cont.) However, not all social species of sweat bees behave like these.  Females of Lasioglossum zephyrum re-emerge in the spring, around mid-April and each one founds her own nest.  She lays eggs in a burrow by herself and then waits for her offspring to grow.  Adults of both sexes emerge in late spring.  During this stage, the colony is subsocial.  Because the first brood of offspring contains both sexes, some of the workers are mated and may occasionally lay eggs.  In June, the foundress queen dies and some of her mated daughters and, possibly, granddaughters begin to lay eggs.  They are called replacement queens.  The colony therefore assumes a quasisocial or semisocial state, with the foundress's female offspring rather hazily divided into (1) house bees, (2) egg layers, and (3) foragers.  After 3 or 4 generations have been produced throughout the season, the organization of the colony breaks up and several of the younger females mate and hibernate.  They will become active the following spring and begin the cycle anew.      
  - There is a new version of the book "Bees of the World" (2004).  The 1991 version was well written and can be found in NYPL! 
Another book : The bees of the world (2000) by Charles Duncan Michener
  - Other than solitary and social bees.  There are cuckoo bees or cleptoparasites forming a distinct category.  (Or cuckoo bee is viewed as an exception in the solitary group.)  The best known one is the cuckoo bumblebees in the genus Psithyrus.



Social Bees

Communal Nests (P) Mason bees, such as Osmia rufa
(A) all known population of the Eurasian Andrena bucephala & A. ferox - The communal nesting habit is restricted (in British bees) to members of the subgenus Hoplandrena, and include the extremely rare Andrena ferox, and the scarce Andrena bucephala.  src   src- a page in Google books
1. share a common nest entrance
2. each bee has her own individual group of cells with the nest.  Like an apartment block, where many occupants share a common ground-floor entrance, but each has his or her own suite of rooms. 
Quasisocial Bees (P) some Indian species of Nomia (e.g., here) 1. share a common nest entrance
2. all of them foraging for nectar and pollen
3. all the females belonging to the same generation, and are mated
4. all being egg layers
5. the building, lining and provisioning of a cell involves the work of more than one female.  But only one female gets to lay an egg in any one cell.  Like a religion community living in an apartment, where each has his or her own family and suite of rooms, but they help each others to decorate and maintain the rooms, and to rear and babysit the children.
Semisocial Bees large, metallic halictid mining bees of the genus Pseudaugochloropsis from the neotropics (e.g., here & here) 1. not all being egg layers.  There is a division of labor: a caste of egg-layers (queens) which do little or no foraging, and a caste of foragers (workers) which do little or no egg laying.  Analogy: a traditional Chinese wealthy big family with many wives and slaves of female workers.  Those wives and female workers are not related genetically; and the female workers are not brought up by any of the wives.  They are about the same age. 
2. all the females belonging to the same generation.
All the above 3 categories are conveniently called Parasocial.  The new generation of females in a parasocial colony usually overwinter in their natal nests and remain with them in the following season.  In tropical areas, there may be 2 or more generations per year, with little or no overlap between them.  In either case, a proportion of females in a new generation leave their natal nests (so not ALL 'remain with them', some leave and build a new home) and excavate new ones of their own where they may be joined later by other females.  
Subsocial Bees Small Carpenter Bee, Ceratina 1. not all the females belonging to the same generation; but typically, the mother dies when the offspring become adult.  So there is only one adult mated female.  It is a family group comprising a female bee & her immature offspring. 
2. A subsocial nest differs from parasocial nests in that there is direct association between the adult females and the immature stages of the next generation, in the form of some sort of maternal care.  Analogy: a woman bears or adopts many daughters.  When one generation dies, the next generation takes over the household.  But before it, the adult woman and the teenager girls are lived together.  So it is a family with no outsider.
3. When the bees of the first egg batch reach adulthood, one or more of them normally remains behind to help the mother raise the next generation.  If this happens, then the colony has passed from the subsocial to the eusocial level.    
A eusocial colony comprises an egg-laying queen and 2 or more generations of adult females which function as workers.
Primitively Eusocial Bees bumble bees
sweat bees (Halictidae), e.g., Lasioglossum zephyrum
1. always founded by a single, mated female, and thus passes through early solitary and subsocial phases.  But in some cases, a founding female may be joined by other females of the same generation and the colony may pass through a semisocial phase until the original female has asserted dominance and the joiners cease to lay eggs.
  case #1: founder alone all the time: solitary > subsocial > this.
  case #2: founder + joiners: solitary > semisocial > this.
2. so ending up is only one queen.
3. Because passing through solitary and subsocial phase, it is temporarily eusocial; in contrast to the highly or permanently eusocial.
Eusocial Bees stingless bees
honey bees
1. the new colonies are organized by the workers.

Note: P - perhaps, some evidence & observations, may, occasionally, some not all the species; A - (nearly) all known species, fixed characteristic, norm.

here has a good summary:

Levels of Sociality

  1. Solitary

  2. Parasocial

    Communal - adults of one generation use a composite nest

    Quasisocial - (above) and cooperate in brood care

    Semisocial - same as quasisocial but some work and others reproduce (castes)

  3.  Subsocial - adults care for young

    Subsocial I - mother and daughters live in same nest

    Subsocial II - type I and cooperate

  4. Eusocial - cooperative brood care, reproductive castes, overlap of generations

Eusociality can be reached via Subsocial II or Semisocial stages


Is this schema also in wasps, ants and other insects? 

Subsocial insects   mirror  


Bees and Social Insects

1. Definition of Eusociality

Many animals live together as a group, but they are not necessarily social (e.g. a school of fish) because there is a very precise definition when it comes ot sociality. True sociality (eusociality) is defined by three features: 1). There is cooperative brood-care so it is not each one caring for their own offspring, 2). There is an overlapping of generations so that the group (the colony) will sustain for a while, allowing offspring assist parents during their life, and 3). That there is a reproductive division of labor, i.e. not every individual reproduces equally in the group, in most cases of insects, this means there is one or a few reproductive(s) ("queen", or "king"), and workers are more or less sterile.

2. Degrees of sociality

Obviously not all insects are eusocial. Michener (1969) provided some other classifications of various stages of social insects:

  1. Solitary: showing none of the three featured we mentioned above (most insects)
  2. Subsocial: the adults care for their own young for some period of time (cockroaches)
  3. Communal: insects use the same composite nest without cooperation in brood care (digger bees)
  4. Quasisocial: use the same nest and also show cooperative brood care (Euglossine bees)
  5. Semisocial: in addition to the features in quasisocial, also has a worker caste (Halictid bees)
  6. Eusocial: in addition to the features of semisocial, there is overlap in generations (Honey bees).

3. A survey of eusocial animals

Eusociality was considered extremely rare in the whole animal kingdom, and even in insects it was only found in Hymenoptera (ants, bees, and wasps) and Isoptera (termites). However, recently this has expanded to a few more groups: in gall aphids (Homoptera) there are sterile soldiers who would sacrifice their lives to their clone sisters who can reproduce, so they are considered eusocial because these soldiers do not reproduce while others do. This is also the case for social thrips that are gall-forming (Thysanoptera). In 1992 a social weevil ( Austroplatypus incompertus, Curculionidae Coleoptera).was discovered. In non-insects, eusociality only appeared twice: in a mammal and a marine animal. Naked mole rats live in complex underground tunnel systems in Africa and animals in the same nest are closely related, only one female (the queen) reproduces, although workers, normally sterile, can ovulate when removed from the nest, presumably due a lack of inhibition from the queen. Snapping shrimp (Synalpheus regalis) lives inside sponges and each ‘colony’ has 200-300 individuals, but only one queen reproduces, again the caster is probably not fixed — the workers remain totipotent and can potentially become a queen when the queen shrimp is removed.

The table below summarizes the above information. Notice that "the number of times eusociality has evolved" does not mean the number of cases of eusociality (there would be tens of thousands if so, because there are about 9 thousand species, of ants alone). Instead it means how many times it has independently evolved (for example, there are 9 species of honey bees, if all of them shared a common eusocial ancestor, it would be considered to be evolved once here, actually you trace back to the lower branch of the taxonomic tree, and count only once at the lowest level).

    Table 1.1. Taxa of insects and the number of times eusociality has evolved within each.

     Insect Orders  Common Names Frequency of Evolution of Eusociality
     Hymenoptera  Ants, bees, & wasps 11
     Isoptera  Termites 1
     Homoptera  Gall-forming aphids * 1
     Coleoptera  Bark-nesting weavils 1
     Thysanoptera  Gall-forming thrips * 1
     Non-insects  Snapping shrimps and naked mole rats 2
     Total   17
    * These 2 insects have recently been classified as eusocial because of the presence of a sterile guard caste.  However, this form of restricted eusociality differs in important ways from the eusocial condition of Hymenoptera.  The guard caste is the only non-reproductive caste in aphid and thrips societies, and the guards do not care for the young.

Within the Hymenoptera, eusociality is found in all ants (Formicidae), vespid wasps (Vespidae), and some bees (Aptidae).  Members of the subfamilies Bombinae (i.e., bumblebee), Meliponinae, and Apinae are eusocial. 

 (Encyclopedia of insects 2009 By Vincent H. Resh, Ring T. Cardé 

I have the 2003 version at: H:\siung_Download\

City Bees Newly Discovered

This small guy Andrena carlini look like Eastern Carpenter Bee ( Xylocopa virginica ) but smaller than it:

Name Group Level of Sociality Size / appearance / Id  Misc. 
European/Western/Common Honey Bee
(Apis mellifera)
Honey Bee Eusocial
Brown-belted Bumble Bee
(Bombus griseocollis)
Bumble Bee - 熊蜂属 (Bombus) Primitively Eusocial    
Eastern Carpenter Bee
( Xylocopa virginica )
Carpenter Bee Carpenter Bees are traditionally considered solitary bees, though some species have simple social nests in which mothers and daughters may cohabit. look similar to Bumble Bee  
Small Carpenter Bee
 Ceratina   wiki
  Solitary / Subsocial smaller  
Sweat Bee
  Solitary / Primitively Eusocial smaller  
Giant Resin Bee
Megachile sculpturalis )
leafcutting bee 切葉蜂 family, Megachilidae Solitary smaller. Its abdomen is not hairy, neither is it shiny like that of a carpenter bee.  Both carpenter bees and giant resin bees nest above ground in wood, but carpenter bees excavate their own tunnels, while the giant resin bee locates and occupies tunnels made by other insects.


Megachile, Leaf-Cutter Bees at Flatbush, Brooklyn
Like carpenter bees, Leaf-cutters are solitary bees that outfit their nests in tunnels in wood. Unlike carpenter bees, they're unable to chew out their own tunnels, and so rely on existing ones. This year, I've observed a large leaf-cutter - yet to be identified - reusing a tunnel bored in previous years by the large Eastern carpenter bee, 
Xylocopa virginica.

An unidentified Megachile, leaf-cutter bee, I found in my garden.