Bumble Bees (lat. Bombus)

Phylogeny

The bumblebee tribe Bombini is one of four groups of corbiculate bees (those with pollen baskets) in the Apidae, the others being the Apini (honey bees), Euglossini (orchid bees), and Meliponini (stingless bees). The corbiculate bees are a monophyletic group. Advanced eusocial behaviour appears to have evolved twice in the group, giving rise to controversy, now largely settled, as to the phylogenetic origins of the four tribes; it had been supposed that eusocial behaviour had evolved only once, requiring the Apini to be close to the Meliponini, which they do not resemble. It is now thought that the Apini (with advanced societies) and Euglossini are closely related, while the primitively eusocial Bombini are close to the Meliponini, which have somewhat more advanced eusocial behaviour. Sophie Cardinal and Bryan Danforth comment that “While remarkable, a hypothesis of dual origins of advanced eusociality is congruent with early studies on corbiculate morphology and social behavior.” Their analysis, combining molecular, morphological and behavioural data, gives the following cladogram:

On this hypothesis, the molecular data suggest that the Bombini are 25 to 40 million years old, while the Meliponini (and thus the clade that includes the Bombini and Meliponini) are 81 to 96 million years old, about the same age as the corbiculate group. However, a more recent phylogeny using transcriptome data from 3,647 genes of ten corbiculate bee species supports the single origin of eusociality hypothesis in the corbiculate bees. They find that Bombini is in fact sister to Meliponini, corroborating that previous finding from Sophie Cardinal and Bryan Danforth (2011). However, Romiguier et al. (2015) shows that Bombini, Meliponini, and Apini form a monophyletic group, where Apini shares a most recent common ancestor with the Bombini and Meliponini clade, while Euglossini is most distantly related to all three, since it does not share the same most recent common ancestor as Bombini, Meliponini, and Apini. Thus, their analysis supports the single origin of eusociality hypothesis within the corbiculate bees, where eusociality evolved in the common ancestor of Bombini, Apini, and Meliponini. The fossil record for bees is limited, with around 14 species that might possibly be Bombini having been described by 2019. The only Bombus relatives in Bombini are the late Eocene Calyptapis florissantensis from the Florissant Formation, USA, and Oligobombus cuspidatus from the Bembridge Marls of the Isle of Wight. Two species of Bombus have been described from the Oligocene of Beşkonak, Bucak Turkey: Bombus (Mendacibombus) beskonakensis and Bombus (Paraelectrobombus) patriciae. Both species were originally placed in genera considered at the time of description as outside of Bombus, being initially named Oligoapis beskonakensis and Paraelectrobombus patriciae respectively, however reexaminiation of the fore-wings lead to both being considered as Bombus species In 2012 a fossil bumblebee from the Miocene was found in Germany’s Randeck Maar and classified as Bombus (Bombus) randeckensis. In 2014, another species, Bombus cerdanyensis, was described from Late Miocene lacustrine beds of La Cerdanya, Spain, but not initially placed into any subgenus, The species Bombus trophonius was described in October 2017 and placed in Bombus subgenus Cullumanobombus. A redescription of the Bombini fossil record by Dehon et al (2019) resulted in the synonymization of the genus Oligoapis with Bombus subgenus Mendacibombus, and the placement of genus Paraelectrobombus as Bombus subgenus Paraelectrobombus, rather than as a genus in Electrobombini. The subgenus Cullumanobombus was expanded to include not only Bombus trophonius but also Bombus randeckensis which was moved from subgenus Bombus and Bombus pristinus, first described by Unger (1867). Within the subgenus Melanobombus only Bombus cerdanyensis is present from the fossil record. An additional three species, “Bombus” luianus, “Bombus” anacolus and “Bombus” dilectus have been attributed to Bombus from the Middle Miocene Shanwang formation of China by Zhang, (1990) and Zhang et al (1994). Due to not being able to study Zhang’s type specimens, but only illustrations of the fossils, Dehon et al did not place the three species within any specific subgenera, and considered all three as “species inquirenda”, needing fuller re-examination. Two other species were not examined at all by Dehon et al, Bombus? crassipes of the Late Miocene Krottensee deposits in the Czech Republic, and Bombus proavus from the Middle Miocene Latah Formation, USA.

General description

Bumblebees vary in appearance, but are generally plump and densely furry. They are larger, broader and stouter-bodied than honeybees, and their abdomen tip is more rounded. Many species have broad bands of colour, the patterns helping to distinguish different species. Whereas honeybees have short tongues and therefore mainly pollinate open flowers, some bumblebee species have long tongues and collect nectar from flowers that are closed into a tube. 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 22 mm (0.9 in) long, males up to 16 mm (0.6 in) long, and workers between 11 and 17 mm (0.4–0.7 in) long. The largest bumblebee species in the world is B. dahlbomii of Chile, up to about 40 mm (1.6 in) long, and described as “flying mice” and “a monstrous fluffy ginger beast”.

Predators, parasites, and pathogens

Bumblebees, despite their ability to sting, are eaten by certain predators. Nests may be dug up by badgers and eaten whole, including any adults present. Adults are preyed upon by robber flies and beewolves in North America. In Europe, birds including bee-eaters and shrikes capture adult bumblebees on the wing; smaller birds such as great tits also occasionally learn to take bumblebees, while camouflaged crab spiders catch them as they visit flowers.

The great grey shrike is able to detect flying bumblebees up to 100 m (330 ft) away; once captured, the sting is removed by repeatedly squeezing the insect with the mandibles and wiping the abdomen on a branch. The European honey buzzard follows flying bees back to their nest, digs out the nest with its feet, and eats larvae, pupae and adults as it finds them. Bumblebees are parasitised by tracheal mites, Locustacarus buchneri; protozoans including Crithidia bombi and Apicystis bombi; and microsporidians including Nosema bombi and Nosema ceranae. The tree bumblebee B. hypnorum has spread into the United Kingdom despite hosting high levels of a nematode that normally interferes with queen bees’ attempts to establish colonies. Deformed wing virus has been found to affect 11% of bumblebees in Great Britain. Female bee moths (Aphomia sociella) prefer to lay their eggs in bumblebee nests. The A. sociella larvae will then feed on the eggs, larvae, and pupae left unprotected by the bumblebees, sometimes destroying large parts of the nest.