About Bombus terrestris (Linnaeus, 1758)
Bombus terrestris is a species of pollen-storing bumblebee that feeds and forages on nectar and pollen. Adults of this species have different body lengths depending on their caste: queens measure 20 to 22 mm long, males measure 14 to 16 mm, and workers measure 11 to 17 mm. B. terrestris workers have abdomens with white tips, and closely resemble workers of the related white-tailed bumblebee B. lucorum. The only distinguishing feature when compared directly is that the yellowish body bands of B. terrestris are darker. B. terrestris queens have a buff-white abdomen tip, or tail, which matches the species' common name, while B. lucorum queens share the solid white abdomen tip seen in B. lucorum workers. Unlike other bees, B. terrestris worker castes have very wide size variation: worker thorax lengths range from 2.3 to 6.9 mm, and worker masses range from 68 to 754 mg. B. terrestris is most commonly found across Europe, where it generally occupies temperate climates. It can survive in a wide range of habitats, so populations also exist in the Near East, Mediterranean Islands, and Northern Africa. The species was introduced to non-native regions as a greenhouse pollinator, and many escaped populations have become established. As a result, B. terrestris is now considered an invasive species in many of these non-native areas, including Japan, Chile, Argentina, and Tasmania. This species usually builds its nests underground, most often in abandoned rodent dens. Colonies create comb-like nest structures, with egg cells that each hold several eggs. The queen lays egg cells stacked on top of one another. On average, B. terrestris colonies produce between 300 and 400 bees, with large variation in total worker count. The colony cycle begins with a solitary new queen that hatches from an abandoned colony. She mates with a male, finds a suitable nest, and overwinters inside this nest. In spring, she lays a small batch of diploid, or female, eggs. After the eggs hatch, the queen tends the larvae and feeds them nectar and pollen. When larvae finish growing, they pupate; the first adult workers emerge approximately two weeks later, marking the end of the colony initiation phase. Workers take over foraging for nectar and pollen for the colony, and care for later generations of larvae. Workers are smaller than the queen, and most die while foraging, killed by predators such as birds or robberflies. Worker foraging range and frequency depend on the quality and distribution of available food, but most workers forage within a few hundred meters of their nest. The initial worker-focused phase can last for varying lengths of time. Once a switch point is reached, the queen begins to lay unfertilized eggs that develop into male drones. When male drones leave the nest, they do not return, and only forage to feed themselves. They search for newly emerging queens to mate with. The remaining diploid eggs hatch into larvae that receive extra food, and pupate to become new queens. The queen uses pheromones to discourage workers from investing extra resources in these new queen larvae, ensuring that only a limited number develop into full queens. The resolution of this worker-queen conflict is complex, and is discussed in further detail elsewhere. In temperate zones, the original colony persists until fall, when workers begin to lay unfertilized eggs that mature into males. At this stage, open aggression breaks out among workers, and between workers and the original queen. This predictable stage occurs about 30 days into the colony cycle in very temperate climates. Usually, worker-queen conflict forces the original queen out of the nest, leaving the colony queenless. A "false queen" may take control of the colony for a short period. Some newly emerged queens temporarily act as workers, helping to raise an additional brood of queens. They leave the nest daily to forage for food, and may mate during this time. Eventually, each new queen finds a location to dig a hibernaculum, where she hibernates until the next spring. When she emerges in spring, she forages to build up her ovaries, then soon searches for a site to start a new nest. In warmer climates, new queens may skip the hibernation stage. The old colony will almost always die out completely; if the old nest site is free of parasites, one of the new queens may return and reuse it. Since 1987, B. terrestris has been commercially bred for use as a pollinator for European greenhouse crops, particularly greenhouse tomatoes – a task previously done by hand. Commercial rearing of B. terrestris in New Zealand began in the early 1990s, and the species is now used as a commercial pollinator in at least North Africa, Japan, Korea, and Russia. The global trade in B. terrestris colonies likely exceeds 1 million nests per year. In Korea, some producers prefer Bombus ignitus over the already established commercial pollinator B. terrestris, out of concern for competition or genetic contamination from mating with native bumblebee species. North America has implemented a ban on importing B. terrestris, which has led to greater interest in other species such as B. impatiens for commercial pollination there. Even so, B. terrestris remains a key commercial pollinator in Europe. This status has prompted researchers to study how agricultural land affects the species' foraging success and survival. Monoculture farming reduces biodiversity in farmland areas, and likely decreases the number of flowering species available for bees to forage on. As a result, B. terrestris nests grow larger in suburban areas than in farmland, because suburban gardens support greater plant diversity that the bees can feed on. Agriculture has a major impact on many bumblebee species, causing widespread decline in multiple species. However, B. terrestris remains widespread, likely because it can forage over very long distances, making it less sensitive to changes in biodiversity and the environment.
