Bumblebees are a popular and relatively well studied group. Their scientific name is Bombus.
Experts differ in how many kinds exist. The Bombus site of The Natural History Museum, London, lists
238 species among over 2,800 scientific names that have been used at one point or another to describe their diversity.
Geographically their species richness is centered in Asia, Europe, and the New World. For North America, Mexico and Central America,
we recognize 59 kinds, some of which are just distinct forms of highly variable species.
To understand their natural history, it is important to know that
bumblebees have a very unusual genetic system that allows mated females to control the sex of their eggs.
Daughters develop from fertilized eggs; sons, from unfertilized ones.
Unmated females cannot fertilize eggs and can only produce sons.
All other bees and insects in the Hymenoptera group have this genetic system. It is call haplodiploidy.
Most bumblebee queens mate and then start a nest by themselves in the spring.
They first produce worker bees that help the colony grow.
These workers, like all bee, ant and wasp workers, are female.
Although some may lay unfertilized eggs, most do not. They work in the nest, defend it, and forage for pollen and nectar.
In contrast to workers, reproductive females and males are typically produced only at the end of the nesting season.
They do not contribute to their colony's wellbeing for they neither forage nor help in any other ways.
Reproductive females are typically larger than workers and are called queens. Males are called drones, reflecting their work habits,
which are none. Unlike females, which can inflict a painful sting and should not be handled,
drones don't have a stinger to defend even themselves. They gain protection by threat alone, looking like their more dangerous sisters.
Most kinds of bumblebees are social, with queens, workers and drones.
Others, like those placed in the scientific group Psithyrus, have no workers.
Their females try to invade a nest of another bumblebee, kill its queen, and usurp her throne.
You can tell which lifestyle a female leads by her rear legs,
which are only adapted for pollen collection in the kinds that have workers.
The following material taken with permission from: Mitchell, T.B. 1962. Bees of the Eastern United States, Volume II. North Carolina Agricultural Experiment Station. Tech. Bul. No.152, 557 p.
This is a native group of social bees in which the average size is considerably greater than in the honeybees. Both sexes are conspicuously and quite densely hairy insects. Females resemble the honeybee in having the outer surface of the hind tibiae bare and polished, with a marginal fringe of hairs forming the pollen basket or corbicula. In the males also the hind tibiae tend to be somewhat flattened, rather smooth and sparsely pubescent on the outer surface. In the front wing the marginal cell is rather short, separated from the apex of the wing by about its own length. In the hind wing the jugal lobe is absent. Usually there is a quite distinct and often extensive malar space separating the lower end of the eye from the mandible. The gonostyll of the male genital armature are very short in the majority of species, extending only slightly beyond the tips of the gonoeoxites and penis valves.
In this region these bees are annually social with respect to the organization of the colonies. Newly fecundated queens hibernate during the winter, each one starting a new colony in the spring. The earlier broods that result from the nest-building, foraging and egg-laying activities of each queen are workers of small size which assume much or all of the foraging and nest-building functions. Thereafter, as the numbers increase, there is an increase in body size of succeeding broods of workers. As the season progresses these more nearly approach the queen in size, and the distinction between the two castes in some species becomes obscure. Finally males and true queens are produced, which mate, and the cycle is repeated.
The species of Bombus occurring in North America do not represent a homogeneous group. They have affinities with those that occur in the Old World and those to the south. In consequence, a natural classification can be achieved only by inclusion of the species of these other regions in comprehensive taxonomic studies. Milliron (1961) indicates that there is evidence of a polyphyletic origin of the group, and therefore he recognizes three separate genera, including a total of five subgenera. All of the other numerous subgenera that have been proposed in the past are being reduced to synonymy. Although it is possible to distinguish these three genera according to the male genital armature, it is very difficult to do so according to the characteristics of the queens or workers. His work is still incomplete, and it has been deemed expedient to avoid the difficulties that would result if an attempt were made to separate these genera in this manual. Thus all the species here are assigned to Bombus in its original, allinclusive sense, recognizing the fact that a division into smaller genera is probable in the future. The following table indicates the classification proposed by Milliron, with respect to the species of this area:
Bombus - affinis and terricola.
Bombias - nevadensis and n. auricomas.
Megabombus - borealis, fervidus and pennsylvanicus.
Cullumanobombus - fraternus, griseocollis and rufocintus.
Pyrobombus - bimaculatus, impatiens, perplexus, sandersoni, ternarius and vagans.
In the males, species assigned to Bombus may be recognized by the flared, dorsoventrally compressed and cup-shaped heads of the penis valves. In Megabombus these structures are straight, either simple or with abrupt, apically dilated heads, while in Pyrobombus they are conspicuously hooked, the curve of the hook directed toward the mid line.
The following keys to the species of Bombus queens, workers and males have limitations due to the degree of variability in these bees. This is especially true of color patterns of the pubescence which are used extensively in the keys. To employ other characters would necessitate the use of more obscure features difficult to describe, or to observe or interpret. Moreover, to account for all the possible variations in color patterns would greatly increase the length and complexity of the keys. In consequence the form in which they appear is a compromise, and it is hoped and believed that they will facilitate identification of the great majority of specimens. A margin of error, however, should be recognized, and where accuracy of identification is of paramount importance, submission of specimens to experienced specialists is recommended.