How Many Bumble Bees In A Colony?



Question: 

How many bumble bees are there in a colony and where do bumble bees raise their colonies?

The short answer is:
Depending on species, most colonies range from small (20 - 100 workers), to large (up to 400 workers).  However, in some countries, there are bumble bee species that can raise a colony with over 1000 workers. 

Some bumble bee species raise their colonies underground.  Several species prefer to nest on patches of moss or tussocks of grass, whilst others prefer to nest above ground.


How Many Bumble Bees In A Colony?

Bombus pascuorum nest showing wax egg cellsA Bombus pascuorum colony nest on a grassy, mossy surface


In his book, Bumblebees Behaviour And Ecology, Professor Dave Goulson comments that in Britain, a large colony size of 100 - 400 workers might be reared by Bombus terrestris (Buff-tailed bumble bee) and Bombus Lapidarius (Red-tailed bumble bee).

In contrast, he notes that small  colonies with 20 - 100 workers are likely for Bombus pascuorum(Common carder), Bombus sylvarum (Shrill Carder bee), Bombus ruderarius (Red-shanked Carder bee), and Bombus muscorum (Moss Carder bee).

Falk provides the following data for approximate nest sizes of British bumble bee species. 

SpeciesCommon NameColony Size
Bombus lucorumWhite-tailed bumble beeOver 200 workers
Bombus terrestrisBuff-tailed bumble bee500 or more individuals
Bombus distinguendusGreat Yellow bumble beeAround 12 workers
Bombus hortorumGarden bumble beeFewer than 100 workers
Bombus humilisBrown-banded Carder bee40 - 50 workers
Bombus hypnorumTree bumble bee150 or more workers
Bombus jonellusHeath bumble beeAbout 50 workers
Bombus lapidariusRed-tailed bumble beeUpto 300 workers
Bombus monticolaBilberry bumble beeFewer than 50 workers
Bombus muscorumMoss Carder bee40 - 120 workers
Bombus pascuorumCommon Carder bee60 - 150 workers
Bombus pratorumEarly bumble beeUpto 100 workers
Bombus ruderariusRed-shanked Carder beeUpto 100 workers,
often significantly fewer
Bombus ruderatusRuderal bumble beeUpto 150 workers
Bombus soreensisBroken-belted bumble bee80 - 150 workers
Bombus subterraneusShort-haired bumble bee75 - 100 workers
Bombus sylvarumShrill Carder beeFewer than 50 workers


Above data compiled from Field Guide to Bees Of Great Britain And Ireland - by Steven Falk.

However, a 2015 study providing data from other regions of the world, including USA and Japan, indicated significant differences in bumble bee colony size.  For example, the colony of Bombus vosnesenskii found in California contained 1848 workers1.

SpeciesColony Size
(Number Of
Workers)
Location of Colonies
(Number In Brackets Indicates
Number Of Colonies
In Study Sample)
Collecting Month
Bombus ardens43Honshu Island, Japan (5)May, June
Bombus atratus54.3Facatativa, Colombia (5);
Loja, Ecuador (2)
February, April, July
Bombus brasilensis42Antonina, Parana, Brazil (1)February
Bombus diversus271.5Honshu Island, Japan (8)June, July, August,
September
Bombus ephippiatus465Monteverde and Volcan Irazu,
Costa Rica (2)
February, July
Bombus honshuensis40Honshu Island, Japan (6)July, August,
October
Bombus huntii515Ruidoso New Mexico, USA (1)August
Bombus hypocrita38Honshu Island, Japan (5)July, August
Bombus ignitus62.5Honshu Island, Japan (8)June, July, August,
September
Bombus impatiens465Michigan, USA (1)August
Bombus lucorum121.2Basel, Switzerland (5)April
Bombus medius800San Luis Potosi, Mexico (1)June
Bombus melaleucus43El Porvenir; Colombia (1)Unreported
Bombus morio67.5Alexandra, Parana, Brazil (2)February
Bombus pennsylvanicus150Willcox, Arizona, USA (1)August, September
Bombus pseudobaicalensis20Hokkaido Island, Japan (1)August
Bombus pullatus336.5San Vito de Java,
Costa Rica (2)
June, July
Bombus schrencki25.5Hokkaido Island, Japan (2)August, September
Bombus terrestris150Hobart, New Zealand (2)February, October
Bombus transversalis118.6Napo River, Ecuador (1);
Tambopata River, Peru (2)
April, October
Bombus vosnesenskii1848Tilden Park, California, USA (1)June

(Table data adapted from Cueva Del Castillo et al, 20151).

What factors affect the size of a bumble bee colony?

Goulson2 found that in general, colony size correlates positively with bumble bees' foraging range, with bee colonies foraging over larger distances generally having bigger colonies.

Also, a large food supply means a larger workforce that will provide more help, including food provisioning, brood care, and defense of the colony, as well as a subsequent increased production of queens (Owen et al. 19803).

Of course, colony size may be impacted by threats to bumble bee nests.

For example, a 2015 study showed that bumble bee colony size was negatively affected by the use of fungicides, resulting in colonies of Bombus impatiens having fewer workers5.

A study of 908 bumble bee nests in Britain between 2008 and 20134, found that colony survival, (measured by success in producing new queens) ranged from as little as 41% for the native Bombus hortorum, to 96% for the recent newcomer, the tree bumble bee, Bombus hypnorum.  

The top 4 reasons for colony failure in order of most commonly occurring, were:

1. excavation of the burrow,
2. human disturbance of the nest, 
3. flooding and 
4. wax moth.

inside a bumble bee nest showing egg cocoons

Do all bumble bees live in colonies?

Yes, although it must be pointed out that cuckoo species do not establish their own, rather they take over colonies established by host queens, often dominating her workers and any food provisions in the nest. 

Where do bumble bees raise their colonies?

Bumble bees, <i>Bombus hypnorum</i> flying around the entrance of a bird nest box.Location of a Bombus hypnorum - in a bird nest box.

Some bumble bee species prefer to make use of burrows underground, such as abandoned mouse holes, but also other crevices may suffice.  Other species, notably the carders, nest on the surface of the ground, typically on tufts of grass and mossy banks.  

Other species nest in tree crevices or even abandoned bird boxes.

Read more about bumble bee nests.

save bee nests

References

1. Cueva Del Castillo R, Sanabria-Urbán S, Serrano-Meneses MA. Trade-offs in the evolution of bumblebee colony and body size: a comparative analysis. Ecol Evol. 2015;5(18):3914-3926. Published 2015 Aug 25. doi:10.1002/ece3.1659.

2. Goulson, D. 2010. Bumblebees, behavior and ecology. Oxford Univ. Press, Oxford, U.K, Pp. 81.

3. Owen, R. E. , Rodd F. H., and Plowright R. C.. 1980. Sex ratio in bumblebee colonies‐complications due to orphaning. Behav. Ecol. Sociobiol. 7:287–291.

4. Goulson, D., O'Connor, S. and Park, K.J. (2018), Causes of colony mortality in bumblebees. Anim Conserv, 21: 45-53. https://doi.org/10.1111/acv.12363.

5. Bernauer OM, Gaines-Day HR, Steffan SA. Colonies of Bumble Bees (Bombus impatiens) Produce Fewer Workers, Less Bee Biomass, and Have Smaller Mother Queens Following Fungicide Exposure. Insects. 2015;6(2):478-488. Published 2015 Jun 1. doi:10.3390/insects6020478.







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