White-tailed Bumble Bee (Bombus lucorum)

 

The White-tailed bumblebee (Bombus lucorum) has, as its name suggests, a white ‘tail’. The rest of the body is black with two bright yellow bands. It looks almost identical to the buff-tailed bumblebee (Bombus Terrestris) which has black and dull yellow bands, and a cream-colored tail. Buff-tailed bumble bee workers also often have white tails. Although difficult to spot, they often have a very faint yellow band in front of the black segment on the abdomen.

Identifying the white-tailed bumble bee from the B. terrestris is even more difficult as there are several sub-species, like the Bombus magnus (northern white-tailed bumble bee) and the Bombus cryptarum (cryptic bumble bee) whose tails often appear slightly brownish or yellowish. Both, queens and workers of all three species are black with a white tail and two lemon-yellow bands.

This cute chunky bee belongs to the Apidae family and is widespread and abundant in Europe, including Island and northern Asia up to the Pacific. Although it can be found in Greece, it has not reached the rest of the Mediterranian. They are generally only aggressive and sting when threatened.

Habitat of the White-tailed bumblebee (Bombus lucorum)

The B. lucorum lives in wide range of habitats. It can be seen in gardens, farm- and grass lands, heath areas, wood clearings and on the edges of woodlands.

Their preferred flowers to forage include Bell Heather and Ling (common heather) in upland areas. In other areas they forage on Bird’s-foot Trefoil, Bramble, Clovers, Dandelions, Knapweed, Scabious, Thistles, and a variety of garden plants.

Nesting Habits

White-tailed bumble bees nest underground. In cooler countries they often build their nests facing south for extra warmth. They often use abandoned rodent nests as a habitat but also use holes in brickwork and overgrown hedgerows for potential nest sites. Queens are often spotted buzzing around exploring nooks and crannies of houses and brickwork.

Unique Traits

Unlike other bumble bee species, B. lucorum have shorter tongues. This enables workers to rob nectar by using the horny sheath around their tongue to make a hole in the flower to reach the nectar. Because they do not enter the flower, they do not come in contact with the pollen.

Colony Structure

B. lucorum nests are very large, containing up to 400 workers. The queen emerges as early as February, beginning of March and is one of the first species of bumble bees to emerge from hibernation. At this time of the year the queen is typically seen flying near the ground looking for suitable nest sites after spending the entire winter underground. To regain the energy she lost during hibernation feeds on nectar to replenish.

Once replenished, she starts to collect pollen on her hind legs, which indicates that she has already found a nest site. The white-tailed bumble bee has large colonies, often containing as many as 400 workers.

Life Cycle of the White-tailed Bumble Bee

Once a suitable nest is found, the queen builds a circular chamber. She constructs an egg cell made from the wax she secretes and lays her first batch of eggs. The nectar she collects is stored in a pot-shaped structure made of wax and placed in front the egg cell to provide her with sufficient energy to incubate the eggs for several days. To keep the eggs warm while sitting on her wax ‘nest’, the queen ´shivers´ her muscles to create heat by contracting and relaxing her muscles. Once the grub-like larvae emerges, the queen forages for nectar and pollen to feed her offspring.

After approximately two weeks the larvae turn into pupae. The first brood consists exclusively of workers. Until the first workers hatch, the queen has to tend for her brood and forage all by herself. Once the first workers emerge, they will take over the foraging, brood tending and all other duties, relieving the queen to focus on laying eggs. She continues to produce workers until later in the season, when she produces new queens and males (drones) to allow the colony to reproduce.

New Queens and Drones

The workers begin to emerge between late March and mid May, whereas new queens and males do not start to emerge until August once the colony has reached a sufficient quantity. The emergence of new queens and drones signals the beginning of the end of the colony. The old queen and the workers die naturally around autumn time.

Both, the new queens and drones (males) will leave the nest once fully developed to reproduce. The new drones will perish soon after mating with the new queens, while the new queens find a place to hibernate over winter and the cycle repeats itself.

Mating Process

Once the males are fully developed, they leave the nest. They fly patrolling circuits around tree-top hight to deposit pheromones on the ground to attract new queens. Although the actual mating usually takes place on the ground or on vegetation, it also sometimes appears to occur in flight. At the beginning of the mating process, the drone grabs the queen´s thorax to bring himself into the right position.

Soon after the mating process the drones die, whereas the freshly mated new queens go out to forage. They feed heavily on pollen and nectar to store fat that is used to provide energy during a long hibernation.

Predators and Diseases of the White-tailed Bumble Bee

Badgers, the primary mammalian predators, use their sharp claws to unearth nests filled with larvae and sustenance stores. Predation is more likely to occur in arid conditions as badgers have a tougher time foraging for their favorite food – worms. Larger nests are usually targeted, since the badgers are able to sniff them out with more ease. By the time these nests are attacked, they’re likely to have produced new reproductive individuals.

Birds also take a toll on bumblebee populations. Some of the most common bird predators are cuckoos and great tits, who prey on the larvae and eggs of bees. Other birds, such as magpies and corvids, sometimes eat adult bumblebees too. Research has shown that the number of bumblebee nests attacked by birds increases when there is a shortage of their preferred food source, suggesting that predation pressure from birds may be higher in years when food is scarce.

Finally, there are also some species of parasitic flies which lay their eggs in bumblebee nests, and the larvae then feed on the bee’s larvae. This can significantly reduce the number of new individuals produced by a nest.

These predators, in combination with human-caused threats, can decrease bumblebee populations and impact their success as pollinators. Conservation efforts, from habitat restoration to careful management of pesticides, are critical for maintaining healthy bumblebee populations.