With their fuzzy bodies, long tongues and tireless foraging routine bumblebees are integral parts of our ecosystem. This shot was captured on one of our lavender bushes at home.
Soon, spring and summer will arrive and you will start hearing that buzzing sound again when you go into the garden, walk across a field or meadow with lots of flowers. Every year anew I am fascinated by the small, fluffy and (almost) tireless workers that swarm around the lavender bushes at home.
<span class="firstcharacter">B</span>umblebees have sparked interest in music, e.g. »Flight of the Bumblebees« by Nikolai Rimsky-Korsakov, in literature and poetry of authors such as J. K. Rowling and J. R. R. Tolkien which used the name Dumbledore (an 18th-century word for the little insect) or in popular culture like the »Transformers« franchise’s fictional character Bumblebee.
With over 250 species and millions of artificially created nests around the world to ensure fruit and vegetable production bumblebees are essential for the survival of various ecosystems and the stability of agriculture.
1. Unique in pollination
As a reminder: The vast majority of flowering plants that produce fruits, seeds, and flowers need to be pollinated during every cycle in order to reproduce. Animals and wind remain the major pollination methods. Only a minority of plants can reproduce using different kinds of reproduction such as cloning.
Bumblebees are crucial in that regard, especially in cooler climates and lower light conditions where other pollinators like honeybees might struggle. They can regulate their body temperature through shivering, allowing them to remain active in cooler environments.
The fluffy insects perform »buzz pollination«, where they vibrate flowers to release trapped pollen, a process that many plants like tomatoes or blueberries require. Certain flowers, like the bottle gentian, have evolved to be pollinated exclusively by bumblebees due to their size and strength. They are also twelve times more effective than honeybees when collecting nectar and are much more efficient since they can collect nectar and pollen at the same time.
Their asynchronous muscles let their wings beat over 130 times per second to carry their heavy loads around.
Bumblebees have an advantage in pollination because of their fuzzy bodies, which allow them to carry large amounts of pollen between plants. Their hairy tongue is also much longer than that of honeybees allowing them to access more tube-shaped plants such as foxgloves or certain orchids while foraging. Unfortunately, in some populations their tongue is becoming shorter generation after generation due to climate change. The reason is the disappearance of many flower species.
They have five eyes - three smaller simple eyes (ocelli) located on the top of their head for light detection and two large compound eyes on the sides of their head, which are responsible for detecting movement, light, and colour. Their unique features and foraging behaviour which they pursue up to 18 hours per day foster biodiversity and agricultural productivity, including special crops and wildflowers.[1, 2]
2. Social Setup and key differences to honeybees
Both bumblebees and honeybees are members of the bee family.
While bumblebees have a well-organized social structure, overall it’s much simpler than that of honeybees. Honeybee colonies can consist of up to 50,000 individuals – bumblebee colonies are significantly smaller, typically housing only 50 to a few hundred individuals. Contrary to honeybee colonies, bumblebees lack complex nest structures. Their nests are simpler, limited by the size of pre-existing cavities.
<strong style="color: #008091;">They are also divided in three castes: </strong>
<span style="color: #008091;">The queen bee</span>, male drones and sterile female worker bees. The queen is the only fertile bee in both genera although honeybee queens can live several years whereas bumblebee queens only live up to one year.
Unlike <span style="color: #008091;">the workers</span> of honeybees which are bound to an intricate system of labour division that includes specific roles such as nurse bees, foragers, and hive cleaners, the worker bumblebees are jacks of all trades. They perform all non-reproductive tasks. They also defend the nest or hive – but only honeybee workers will lose their sting after using it and mostly die afterwards. Both honeybee and bumblebee workers have similar lifespans of a few weeks.
<span style="color: #008091;">Male drones</span> only exist to mate with the queen and honeybee drones are expelled before winter to conserve resources. Bumblebee drones have a much shorter lifespan.
Bumblebee colonies are annual, meaning they die off at the end of the season, with only the queen surviving through hibernation. In contrast, honeybee colonies are perennial, with the colony surviving year-round.
Moreover, bumblebees communicate primarily through pheromones and physical interactions within their colony, while honeybees use the waggle dance to communicate the location of food sources to other members of the hive.
Bumblebees can mark already-pollinated flowers by leaving individual scent trails through their feet.[3]
3. population decline
Bumblebee populations have been experiencing significant declines across Europe, North America, and Asia.
Contributing factors include rising temperatures due to climate change, habitat loss because of land-use changes that reduce their food plants, the mechanization of agriculture leading to the loss of flower-rich meadows, and increased pesticide use adversely affecting their health. Especially agriculturally used neonicotinoids (neurotoxins) have remained a big threat to their lives. In North America, pathogens have also been identified as a significant issue.
The ongoing decline has led to the extirpation of several bumblebee species in regions like Britain and Ireland, with others facing serious threats to their populations.
The population of the American bumblebee has dropped by 90% over the last two decades and the white-tailed and red-tailed bumblebee populations fell by 60% and 74% in the UK, respectively.
The reduction in bumblebee numbers poses a risk to ecosystem health and agricultural stability, as these insects play a crucial role in pollinating plants. This means that in addition to fixing the climate crisis we need to make rapid changes to our agricultural system – otherwise it is likely to collapse in the near future. Another side effect of climate change are alterations in climate patterns which disrupt the timing of flowering plants and bumblebee activity, disrupting their usual foraging and nesting behaviors.[4, 5]
Luckily, conservation efforts are underway to combat some of the worst effects. One rewilding project at Denmarkfield in Scotland transformed former barley fields into diverse habitats, resulting in a remarkable increase in bumblebee numbers – from 35 individuals in 2021 to 4,056 in 2023 – and a doubling of species diversity.[6, 7]
In Germany projects involve habitat restoration and creation, increased monitoring efforts, the promotion of pesticide-free practices public awareness campaigns. The focus is mostly on bees but also includes bumblebees. The fine for killing, catching or disturbing bumblebees in any way can be as high as 65,000€.[8, 9, 10, 11, 12, 13]
One of the things I found most surprising is that there are so-called cuckoo bumblebees (psithyrus) which are a subgenus of bumblebees (bombus) and known for their socially parasitic behavior.
Unlike typical bumblebees, Cuckoo bumblebees lack pollen-collecting hairs and do not have worker bees in their colonies; their colonies consist only of drones and queen-like females. These parasitic bees infiltrate the nests of other bumblebee species, where they lay their eggs, often after fighting with the resident workers and devouring the host queen’s eggs. The larvae that hatch do not contribute to foraging or brood care, instead, they rely on the host colony for food. They have a more limited range and are rarer than their host species, often facing a higher risk of extinction. Their presence can weaken or kill the host queen due to neglect from the workers.
Cuckoo bumblebees lack a pollen basket on their rear legs, do not exude wax from their abdomen, have a less hairy body and a more pointed abdomen, possess a harder exoskeleton, a longer sting than queen and worker bumblebees, and a short tongue, making them nearly impervious to stings during fights due to the absence of weak points in their body. They cannot produce wax or honey, rely on host colonies to care for their brood, and while their parasitic behaviour may seem harmful, they play an important ecological role in shaping populations, biodiversity, and the resilience of ecosystems.[14, 15, 16]
<span class="headingcolor" style="display: block; text-align: center;">Thanks for your attention!</span>
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