Bumblebee - WikiHQ

A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus Bombus, part of Apidae, one of the bee families. This genus is the only extant group in the tribe Bombini, though a few extinct related genera (e.g., Calyptapis) are known from fossils. They are found primarily in the Northern Hemisphere, although they are also found in South America, where a few lowland tropical species have been identified. European bumblebees have also been introduced to New Zealand and Tasmania. Female bumblebees can sting repeatedly, but generally ignore humans and other animals.

Most bumblebees are eusocial insects that form colonies with a single queen. The colonies are smaller than those of honey bees, growing to as few as 50 individuals in a nest. Cuckoo bumblebees are brood parasitic and do not make nests or form colonies; their queens aggressively invade the nests of other bumblebee species, kill the resident queens and then lay their own eggs, which are cared for by the resident workers. Cuckoo bumblebees were previously classified as a separate genus, but are now usually treated as members of Bombus.

Bumblebees have round bodies covered in soft hair (long branched setae) called 'pile', making them appear and feel fuzzy. They have aposematic (warning) coloration, often consisting of contrasting bands of colour, and different species of bumblebee in a region often resemble each other in mutually protective Müllerian mimicry. Harmless insects such as hoverflies often derive protection from resembling bumblebees, in Batesian mimicry, and may be confused with them. Nest-making bumblebees can be distinguished from similarly large, fuzzy cuckoo bumblebees by the form of the female hind leg. In nesting bumblebees, it is modified to form a pollen basket, a bare shiny area surrounded by a fringe of hairs used to transport pollen, whereas in cuckoo bumblebees, the hind leg is hairy all around, and they never carry pollen.

Like their relatives the honeybees, bumblebees feed on nectar, using their long hairy tongues to lap up the liquid; the proboscis is folded under the head during flight. Bumblebees gather nectar to add to the stores in the nest, and pollen to feed their young. They forage using colour and spatial relationships to identify flowers to feed from. Some bumblebees steal nectar, making a hole near the base of a flower to access the nectar while avoiding pollen transfer. Bumblebees are important agricultural pollinators, so their decline in Europe, North America, and Asia is a cause for concern. The decline has been caused by habitat loss, the mechanisation of agriculture, and pesticides.

Etymology

thumb|upright|[[Beatrix Potter's 1910 story The Tale of Mrs. Tittlemouse features a "bumble bee" called Babbity Bumble.

Charles Darwin referred to bumblebees as "humble-bees" in his 1859 book On the Origin of Species, emphasising their importance in pollinating clovers and other wildflowers. The term humblebee remained in use through the nineteenth century, but was gradually replaced by bumblebee in both scientific and common language during the twentieth century.

Evolution

Phylogeny

The tribe Bombini (bumblebees) is one of four lineages of corbiculate bees in the Apidae. It is distinguished by having pollen baskets (corbiculae) on their hind legs. The other three are the Apini (honeybees), Euglossini (orchid bees), and Meliponini (stingless bees). Together they form a monophyletic group.

Early analyses of morphology and behaviour suggested that complex eusociality evolved twice within the corbiculate bees, once in the ancestor of the Apini and once in the Meliponini. Molecular and morphological data indicate that the primitively eusocial Bombini are, despite appearances, closely related to the Meliponini, while the Apini and Euglossini form a separate branch. Cardinal and Danforth (2011) described this dual-origin model as consistent with earlier evidence from social and anatomical traits.

Revisiting the "corbiculate controversy",

The earliest divergence estimates suggest that the Bombini originated between 25 and 40 million years ago, whereas the Bombini–Meliponini clade dates to roughly 80–95 million years ago, around the time the corbiculate group as a whole diversified. The oldest known relatives include Calyptapis florissantensis from the Late Eocene Florissant Formation (United States) and Oligobombus cuspidatus from the Bembridge Marls (Isle of Wight).

Several Oligocene and Miocene species have been assigned to modern subgenera, including Bombus (Mendacibombus) beskonakensis and B. (Paraelectrobombus) patriciae from Turkey, B. randeckensis from Germany, B. cerdanyensis from Spain, and B. trophonius from the Czech Republic.

These fossils indicate that the major subgenera of Bombus were already differentiated by the Miocene and that diversification of the tribe was well underway by the Oligocene. for an overview of the differences between bumblebees and other bees and wasps, see characteristics of common wasps and bees. The genus has been divided variously into up to 49 subgenera, a degree of complexity criticised by Williams (2008). The cuckoo bumblebees Psithyrus have sometimes been treated as a separate genus but are now considered to be part of Bombus. Bumblebees have fewer stripes (or none), and usually have part of the body covered in black fur, while honeybees have many stripes including several grey stripes on the abdomen. Sizes are very variable even within species; the largest British species, B. terrestris, has queens up to long, males up to long, and workers between long. The largest bumblebee species in the world is B. dahlbomii of Chile, up to about long, and described as "flying mice" and "a monstrous fluffy ginger beast".

Distribution and habitat

Abundance and diversity

Bumblebees are most abundant across temperate and montane ecosystems of the Northern Hemisphere, with the greatest species richness found in Eurasia and North America. Bumblebees have a largely cosmopolitan distribution but are absent from Australia (apart from Tasmania, where they have been introduced) and occur in Africa only north of the Sahara. More than a hundred years ago they were also introduced to New Zealand, where they play an important role as efficient pollinators.

At the northern limits of their range, species such as Bombus polaris, B. alpinus, and the parasitic B. hyperboreus occupy Arctic tundra ecosystems that extend as far north as Greenland and Canada's Ellesmere Island. These populations endure some of the planet's shortest flowering seasons and coldest conditions, marking the northernmost boundary of eusocial insect life.

Physiological adaptations

One reason for bumblebee presence in such cold places is that they can regulate their body temperature through several physiological mechanisms. They use solar radiation to warm themselves, generate heat internally through "shivering" known as heterothermy, and employ countercurrent exchange to retain heat. Although other bees show similar forms of thermoregulation, these mechanisms are especially well developed and extensively studied in bumblebees. They also adapt to high-elevation environments by increasing their wing stroke amplitude to sustain flight in thin air.

Biology

thumb|right|upright|A common carder bumblebee [[Bombus pascuorum extending its tongue towards a Heuchera inflorescence]]

Feeding

thumb|thumbtime=28|A [[Bombus vosnesenskii|yellow-faced bumblebee foraging on California poppy]]

The bumblebee tongue (the proboscis) is a long, hairy structure that extends from a sheath-like modified maxilla. The primary action of the tongue is lapping or repeated dipping of the tongue into liquid.

The tip of the tongue probably acts as a suction cup and during lapping, nectar may be drawn up the proboscis by capillary action. When at rest or flying, the proboscis is kept folded under the head. The longer the tongue, the deeper the bumblebee can probe into a flower and bees probably learn from experience which flower source is best-suited to their tongue length. Bees with shorter proboscides, like Bombus bifarius, have a more difficult time foraging nectar relative to other bumblebees with longer proboscides; to overcome this disadvantage, B. bifarius workers were observed to lick the back of spurs on the nectar duct, which resulted in a small reward.

Wax production

The exoskeleton of the abdomen is divided into plates called dorsal tergites and ventral sternites. Wax is secreted from glands on the abdomen and extruded between the sternites where it resembles flakes of dandruff. It is secreted by the queen when she starts a nest and by young workers. It is scraped from the abdomen by the legs, moulded until malleable and used in the construction of honeypots, to cover the eggs, to line empty cocoons for use as storage containers and sometimes to cover the exterior of the nest.

Coloration

thumb|upright|Cuckoo bumblebees, like this [[Bombus barbutellus, have similar aposematic (warning) coloration to nest-making bumblebees, and may also mimic their host species.]]

The black-and-yellow coloration of bumblebees acts as an aposematic (warning) signal to predators, indicating that the insects can inflict a painful sting. This visual warning serves as an anti-predator adaptation that discourages birds and other vertebrates, representing a common example of aposematism among members of the Hymenoptera. Depending on the species and morph, the warning colours range from entirely black, to bright yellow, red, orange, white, and pink. Dipteran flies in the families Syrphidae (hoverflies), Asilidae (robber flies), Tabanidae (horseflies), Oestridae (bot or warble flies) and Bombyliidae (bee flies, such as Bombylius major) all include Batesian mimics of bumblebees, resembling them closely enough to deceive at least some predators.

Many species of Bombus, including the Psithyrus group of cuckoo bumblebees, have evolved a form of Müllerian mimicry. This is a system in which different bumblebee species within the same region share similar warning color patterns, so that a predator only has to learn once to avoid any of them. In California, for example, several largely black species like B. californicus, B. caliginosus, B. vandykei, B. vosnesenskii, B. insularis, and B. fernaldae, form one such mimicry group. Another group in the same region includes species banded in black and yellow. In both cases, the shared coloration gives all members of the group a selective advantage.

Parasitic, or cuckoo, bumblebees also tend to resemble their hosts more closely than would be expected by chance, especially in regions such as Europe where parasite and host species have evolved together. This resemblance is likely another case of Müllerian mimicry, rather than a strategy to deceive the host through aggressive mimicry.

Temperature control

thumb|right|thumbtime=38|Bumblebees can be active in cooler and less favorable weather than most other flying insects. Here it is cool and raining. (with audio)

Bumblebees are active under conditions during which honeybees and other smaller bees stay at home, and can readily absorb heat from even weak sunshine. The thick pile created by long setae (bristles) acts as insulation to keep bumblebees warm in cold weather; species from cold climates have longer setae (and thus thicker insulation) than those from the tropics. The temperature of the flight muscles, which occupy much of the thorax, needs to be at least before flight can take place. The muscle temperature can be raised by shivering. It takes about five minutes for the muscles to reach this temperature at an air temperature of .

Chill-coma temperature

The chill-coma temperature in relation to flying insects is the temperature at which flight muscles cannot be activated. Compared to honey bees and carpenter bees, bumblebees have the lowest chill-coma temperature. Of the bumblebees Bombus bimaculatus has the lowest at . However, bumblebees have been seen to fly in colder ambient temperatures. This discrepancy is likely because the chill-coma temperature was determined by tests done in a laboratory setting. However, bumblebees live in insulated shelters and can shiver to warm up before venturing into the cold.

Bumblebees do not have ears, and it is not known whether or how well they can hear. However, they are sensitive to vibrations transmitted through substrates such as wood or other materials.

Unlike the well-known "dance" communication of honeybees, bumblebees do not perform a spatial waggle or round dance to indicate the location of food sources. Instead, when a forager returns from a successful trip to the nest, it often moves rapidly and excitedly around the nest for several minutes before departing again to forage.

Bumblebees have also been observed to engage in social learning. In experiments with Bombus terrestris, workers were trained to solve a novel task (string-pulling) to obtain a reward, and naïve individuals that observed trained demonstrators were significantly more successful than those that did not. Furthermore, subsequent work showed that novel problem-solving behaviours can spread through bumblebee colonies via social learning under open-diffusion conditions.

Reproduction and nesting

thumb|Nest of red-tailed bumblebee. [[Bombus lapidarius, showing wax pots full of honey]]

Nest size depends on species of bumblebee. Most form colonies of between 50 and 400 individuals, These nests are small compared to honeybee hives, which hold about 50,000 bees. Many species nest underground, choosing old rodent burrows or sheltered places, and avoiding places that receive direct sunlight that could result in overheating. Other species make nests above ground, whether in thick grass or in holes in trees. A bumblebee nest is not organised into hexagonal combs like that of a honeybee; the cells are instead clustered together untidily. The workers remove dead bees or larvae from the nest and deposit them outside the nest entrance, helping to prevent disease. Nests in temperate regions last only for a single season and do not survive the winter.

In the early spring, the queen comes out of diapause and finds a suitable place to create her colony. Then she builds wax cells in which to lay her eggs which were fertilised the previous year. The eggs that hatch develop into female workers, and in time, the queen populates the colony, with workers feeding the young and performing other duties similar to honeybee workers. In temperate zones, young queens (gynes) leave the nest in the autumn and mate, often more than once, with males (drones) that are forcibly driven out of the colony. Many species of bumblebee follow this general trend within the year. Bombus pensylvanicus is a species that follows this type of colony cycle. For this species the cycle begins in February, reproduction starts in July or August, and ends in the winter months. The queen remains in hibernation until spring of the following year in order to optimize conditions to search for a nest.

thumb|left|upright=1.2|Bumblebee life-cycle showing adults and [[larvae in nest of B. terrestris. Engraved in 1840 by William Home Lizars after drawing probably by James Hope Stewart.]]

In fertilised queens, the ovaries only become active when the queen starts to lay. An egg passes along the oviduct to the vagina where there is a chamber called the spermatheca, in which the sperm from the mating is stored. Depending on need, she may allow her egg to be fertilised. Unfertilised eggs become haploid males; fertilised eggs grow into diploid females and queens. The hormones that stimulate the development of the ovaries are suppressed in female worker bees, while the queen remains dominant.

thumb|An above-ground nest, hidden in grass and moss, of the common carder bee, [[Bombus pascuorum. The wax canopy or involucrum has been removed to show winged workers and pupae in irregularly placed wax cells.]]

After the emergence of the first or second group of offspring, workers take over the task of foraging and the queen spends most of her time laying eggs and caring for larvae. The colony grows progressively larger and eventually begins to produce males and new queens.

Bumblebee workers can lay unfertilised haploid eggs (with only a single set of chromosomes) that develop into viable male bumblebees. Only fertilised queens can lay diploid eggs (one set of chromosomes from a drone, one from the queen) that mature into workers and new queens.

In a young colony, the queen minimises reproductive competition from workers by suppressing their egg-laying through physical aggression and pheromones. Worker policing leads to nearly all eggs laid by workers being eaten. Because of the reproductive competition between workers and the queen, bumblebees are considered "primitively eusocial".

Although a large majority of bumblebees follow such monogynous colony cycles that only involve one queen, some select Bombus species (such as Bombus pauloensis) will spend part of their life cycle in a polygynous phase (have multiple queens in one nest during these periods of polygyny).

Foraging behaviour

thumb|left|A bumblebee loaded with [[pollen in its pollen baskets]]

alt=A bumblebee loaded with pollen flying to a flower|thumb|A bumblebee loaded with [[pollen flying to a Crocus ]]

thumb|[[Bombus vosnesenskii|Yellow-faced bumblebee foraging California lilac. Repeated a second time at one-fourth speed.]]

Bumblebees generally visit flowers that exhibit the bee pollination syndrome and these patches of flowers may be up to 1–2 km from their colony. They tend to visit the same patches of flowers every day, as long as they continue to find nectar and pollen there, a habit known as pollinator or flower constancy. While foraging, bumblebees can reach ground speeds of up to .

Bumblebees use a combination of colour and spatial relationships to learn which flowers to forage from. They can also detect both the presence and the pattern of electric fields on flowers, which occur due to atmospheric electricity, and take a while to leak away into the ground. They use this information to find out if a flower has been recently visited by another bee. Bumblebees can detect the temperature of flowers, as well as which parts of the flower are hotter or cooler and use this information to recognise flowers. After arriving at a flower, they extract nectar using their long tongues ("glossae") and store it in their crops. Many species of bumblebees also exhibit "nectar robbing": instead of inserting the mouthparts into the flower in the normal way, these bees bite directly through the base of the corolla to extract nectar, avoiding pollen transfer.

Pollen is removed from flowers deliberately or incidentally by bumblebees. Incidental removal occurs when bumblebees come in contact with the anthers of a flower while collecting nectar. When it enters a flower, the bumblebee's body hairs receive a dusting of pollen from the anthers. In queens and workers this is then groomed into the corbiculae (pollen baskets) on the hind legs where it can be seen as bulging masses that may contain as many as a million pollen grains. Male bumblebees do not have corbiculae and do not purposively collect pollen. Bumblebees are also capable of buzz pollination, in which they dislodge pollen from the anthers by creating a resonant vibration with their flight muscles.

In at least some species, once a bumblebee has visited a flower, it leaves a scent mark on it. This scent mark deters bumblebees from visiting that flower until the scent degrades. This scent mark is a general chemical bouquet that bumblebees leave behind in different locations (e.g. nest, neutral, and food sites), and they learn to use this bouquet to identify both rewarding and unrewarding flowers, and may be able to identify who else has visited a flower. Bumblebees rely on this chemical bouquet more when the flower has a high handling time, that is, where it takes a longer time for the bee to find the nectar once inside the flower.

Once they have collected nectar and pollen, female workers return to the nest and deposit the harvest into brood cells, or into wax cells for storage. Unlike honeybees, bumblebees only store a few days' worth of food, so are much more vulnerable to food shortages. Male bumblebees collect only nectar and do so to feed themselves. They may visit quite different flowers from the workers because of their different nutritional needs.

Asynchronous flight muscles

Bees beat their wings about 200 times a second. Their thorax muscles do not contract on each nerve firing, but rather vibrate like a plucked rubber band. This is efficient, since it lets the system consisting of muscle and wing operate at its resonant frequency, leading to low energy consumption. Further, it is necessary, since insect motor nerves generally cannot fire 200 times per second. These types of muscles are called asynchronous muscles and are found in the insect wing systems in families such as Hymenoptera, Diptera, Coleoptera, and Hemiptera.

Cuckoo bumblebees

thumb|upright=0.9|The cuckoo bumblebee B. vestalis, a parasite of B. terrestris

Bumblebees of the subgenus Psithyrus (known as 'cuckoo bumblebees', and formerly considered a separate genus) are brood parasites, sometimes called kleptoparasites, in the colonies of other bumblebees, and have lost the ability to collect pollen. Before finding and invading a host colony, a Psithyrus female, such as that of the Psithyrus species of B. sylvestris, feeds directly from flowers. Once she has infiltrated a host colony, the Psithyrus female kills or subdues the queen of that colony, and uses pheromones and physical attacks to force the workers of that colony to feed her and her young. Usually, cuckoo bumblebees can be described as queen-intolerant inquilines, since the host queen is often killed to enable the parasite to produce more offspring,

The female Psithyrus has a number of morphological adaptations for combat, such as larger mandibles, a tough cuticle and a larger venom sac that increase her chances of taking over a nest. Upon emerging from their cocoons, the Psithyrus males and females disperse and mate. The males do not survive the winter but, like nonparasitic bumblebee queens, Psithyrus females find suitable locations to spend the winter and enter diapause after mating. They usually emerge from hibernation later than their host species. Each species of cuckoo bumblebee has a specific host species, which it may physically resemble. In the case of the parasitism of B. terrestris by B. (Psithyrus) vestalis, genetic analysis of individuals captured in the wild showed that about 42% of the host species' nests at a single location

The origin of this claim has been difficult to pin down with any certainty. John H. McMasters recounted an anecdote about an unnamed Swiss aerodynamicist at a dinner party who performed some rough calculations and concluded, presumably in jest, that according to the equations, bumblebees cannot fly.

In later years, McMasters backed away from this origin, suggesting there could be multiple sources, and stating that the earliest he had found was a reference in the 1934 book ' by French entomologist Antoine Magnan (1881–1938). Magnan had applied the equations of air resistance to insects, giving the result that their flight would be impossible, but "One shouldn't be surprised that the results of the calculations don't square with reality". The following passage appears in the introduction to Le Vol des Insectes:

Magnan refers to his assistant André Sainte-Laguë. Some credit physicist Ludwig Prandtl (1875–1953) of the University of Göttingen in Germany with popularizing the idea. Others say Swiss gas dynamicist Jakob Ackeret (1898–1981) did the calculations.

thumb|Bumblebee in flight. It has its tongue extended and a laden pollen basket.

The calculations that purported to show that bumblebees cannot fly are based upon a simplified linear treatment of oscillating aerofoils. The method assumes small amplitude oscillations without flow separation. This ignores the effect of dynamic stall (an airflow separation inducing a large vortex above the wing), which briefly produces several times the lift of the aerofoil in regular flight. More sophisticated aerodynamic analysis shows the bumblebee can fly because its wings encounter dynamic stall in every oscillation cycle.

The evolutionary biologist John Maynard Smith pointed out that bumblebees would not be expected to sustain flight, as they would need to generate too much power given their tiny wing area. However, in aerodynamics experiments with other insects, he found that viscosity at the scale of small insects meant even their small wings can move a very large volume of air relative to their size, and this reduces the power required to sustain flight by an order of magnitude.

In music and literature

The orchestral interlude Flight of the Bumblebee was composed (c. 1900) by Nikolai Rimsky-Korsakov. It represents the turning of Prince Guidon into a bumblebee so he can fly away to visit his father, Tsar Saltan, in the opera The Tale of Tsar Saltan, although the music may reflect the flight of a bluebottle rather than a bumblebee. The music inspired Walt Disney to feature a bumblebee in his 1940 animated musical Fantasia and have it sound as if it were flying in all parts of the theater. This early attempt at "surround sound" was excluded from the film in later showings.

In 1599, during the reign of Queen Elizabeth I, someone, possibly Tailboys Dymoke, published Caltha Poetarum: Or The Bumble Bee, under the pseudonym "T. Cutwode". This was one of nine books censored under the Bishops' Ban issued by the Archbishop of Canterbury John Whitgift and the Bishop of London Richard Bancroft.

Emily Dickinson made a bumblebee the subject of her parody of Isaac Watts's well-known poem about honeybees, "How Doth the Little Busy Bee" (1715). Where Watts wrote "How skilfully she builds her cell! How neat she spreads the wax!", Dickinson's poem, "The Bumble-Bee's Religion" (1881), begins "His little Hearse-like Figure / Unto itself a Dirge / To a delusive Lilac / The vanity divulge / Of Industry and Morals / And every righteous thing / For the divine Perdition / of Idleness and Spring." The letter is said to have enclosed a dead bee.

In 1847, Ralph Waldo Emerson published his poem "The Humble-Bee".

The entomologist Otto Plath wrote Bumblebees and Their Ways in 1934. His daughter, the poet Sylvia Plath, wrote a group of poems about bees late in 1962, within four months of her suicide, transforming her father's interest into her poetry.

thumb|upright|Bumblebees of different species illustrated by [[Moses Harris in his 1782 Exposition of English Insects]]

The scientist and illustrator Moses Harris (1731–1785) painted accurate watercolour drawings of bumblebees in his An Exposition of English Insects Including the Several Classes of Neuroptera, Hymenoptera, & Diptera, or Bees, Flies, & Libellulae (1776–80).

The surname Dumbledore in the Harry Potter series (1997–2007) is an old name for bumblebee. J. K. Rowling said the name "seemed to suit the headmaster, because one of his passions is music and I imagined him walking around humming to himself". J. R. R. Tolkien, in his poem Errantry, used the term Dumbledor for a bumblebee. Among Beatrix Potter's "little books", Babbity Bumble and other members of her nest appear in her 1910 The Tale of Mrs. Tittlemouse.