Buzz Pollinators of the Indian Himalayas

Bumblebees (Bombus spp.) were among the bucket-listed insects I wanted to see and learn about as a young entomologist. In 2019, during my time at the research institution ATREE, I first saw and handled a preserved specimen. That brief encounter felt extraordinary. Later, during my first field visit to Phek district in Nagaland, I saw one alive. It hovered over Cosmos flowers, completely absorbed in foraging, indifferent to my excitement. She was large, fuzzy, and deliberate in her movements, giving off an “I know what I am doing” vibe.

Why did it take me nearly 25 years to see a single bumblebee?

Unlike honeybees, bumblebees are absent from most lowland tropical regions of India. Instead, they occur along the Western and Eastern Himalayas, typically at altitudes between 230 and 4,500 m (largely within 2,000-4,500 m), where temperatures are cooler and seasonal variation is pronounced. In the lowlands of India, carpenter bees (Xylocopa spp.) serve as ecological and functional equivalents of bumblebees.

Indian Himalayan Region: Bumblebee Hotspot

Bumblebees are thought to have originated in Asia, particularly around the Qinghai-Tibetan Plateau, approximately 45 million years ago. This region remains a centre of diversity, and this explains why bumblebees are especially well adapted to Himalayan cold and high-altitude conditions.

All bumblebees belong to a single genus, Bombus, which includes 288 described species worldwide. India hosts 57 species, mainly confined to the Himalayan region, representing 20 per cent of global bumblebee diversity. They range from long-tongued to short-tongued, with body sizes between 7 and 30 mm. Nine species are known to be endemic to this region.

Unlike honeybee colonies, bumblebee colonies are small, annual, and contain around 100-350 individuals. A colony begins with a single queen emerging from hibernation in spring. She establishes a nest, often in abandoned rodent burrows or soil cavities, and raises the first generation of workers. Once workers emerge, they take over foraging and brood care, while she focuses on reproduction. The colony grows through the summer and eventually produces males and future queens. Future queens forage and mate with males from other colonies and enter hibernation, while the rest of the colony dies. In the following spring, the queens emerge, and the cycle continues.

Not all bumblebees are social in nature. Some of them, especially those belonging to the subgenus Psithyrus, are parasitic and are called cuckoo bumblebees. They do not build nests or collect pollen; instead, they invade the colonies of other bumblebees and rely on host workers to rear their offspring.

Bees that change with the environment

Identifying a bumblebee is far more challenging than spotting them. This is due to a fascinating aspect of their biology: phenotypic plasticity. Bumblebees exhibit striking variation in colour, size, and hair density across their altitudinal range. No, it is not diversity across species but variation within species, shaped by environmental conditions such as temperature, altitude, and season.

In the Himalayas, where ecological conditions change sharply over short distances, this variation becomes especially pronounced. Species such as Bombus haemorrhoidalis, B. albopleuralis and B. breviceps occur across a wide altitudinal range from the Western to the Eastern Himalayas. They show noticeable differences in colour patterns and body size between populations. Much of this variation is also tied to Müllerian mimicry, where multiple bumblebee species converge on similar colour patterns to reinforce predator avoidance. As a result, unrelated species in the same region may look remarkably similar, while individuals of the same species may differ across regions.

The science of buzz pollination

One of the most remarkable bumblebee behaviours is buzz pollination. In this process, the bee grips a flower and rapidly vibrates its flight muscles without flapping its wings, producing the distinct buzz. It’s where their scientific name, Bombus (meaning booming), comes from. This vibration dislodges pollen and nectar from flowers. Buzz pollination, combined with their ability to forage under adverse conditions, makes bumblebees highly efficient pollinators and keystone species in many montane ecosystems.

Bumblebees don’t just fly around randomly; they’re constantly reading cues from flowers to decide where to go next. As they fly, their fast wingbeats give them a slight positive charge, while flowers, being connected to the ground, carry a weak negative charge. When a bee lands, it briefly changes this electric field, and other bees can pick up on that, using it as a hint that the flower has already been visited and might not have much left. On top of that, bees also leave behind faint volatile scent marks on flowers, which last up to 40 minutes and act like tiny “visited” signs for others.

How do bumblebees fly?

The first time I was asked how bumblebees fly was not in a lab or a field site, but in a London tavern. A stranger, on learning that I study bees and wasps, leaned in with the question: “Aren’t they supposed to be incapable of flying?”

Bumblebee flight is often described as defying physics! This is not true. Early scientists tried to explain their flight using aeroplane models, which made it seem like bumblebees shouldn’t be able to get off the ground at all. Luckily, the bees don’t fly like planes. Instead, they beat their wings insanely fast (~200 times per second), tracing a tiny figure-eight in the air and creating swirling currents that help keep them aloft. These little whirlpools of air give them the extra lift they need, even though they look a bit too chunky for flight. The result? A bee that can fly in cold, thin mountain air, handle strong winds, and still hover neatly over a flower.

Conditions like cold mornings, dim light, wind and drizzle that would keep most pollinators grounded barely slow them down. They warm themselves by revving their flight muscles like tiny living engines and head out to forage anyway. Unlike honeybees, bumblebees start their job early and keep going late! Their thick, fuzzy hairs act like built-in insulation, and in some species, darker colours help them soak up heat from the sun (thermal melanism). In short, if there’s a flower out there, a bumblebee will probably find a way to reach it.

Threats and conservation

Despite their importance in pollination of both wild and commercial plants, bumblebee populations in India are dwindling. Climate change, land-use change, and pesticide use together are destroying their habitats and affecting their behaviour and survival.

Studies suggest that many bumblebee species are experiencing climate-driven range contractions, increasing their risk of extinction. In regions such as the Himalayas, this can lead to what is often described as an “extinction elevator,” where species are pushed to progressively higher elevations as temperatures rise until they run out of habitats in which to thrive. By 2050, around 72 per cent of Himalayan bumblebee populations are expected to face up to 90 per cent habitat loss. With nowhere left to go beyond the mountaintop, their available habitat shrinks, increasing the risk of local extinction. Conservation efforts must therefore focus on habitat protection, climate-resilient landscapes, and better baseline data on bumblebee diversity and distribution.

Photo source: Bombus breviceps