Bumblebees have an incredible sense of smell to find their way home

Imagine being a bumblebee. Your existence is a vibrant interplay of colors and fragrances, each guiding you as you forage for nectar and pollen. 

It’s a world of excellent vision, where the intricate structure of compound eyes distinguishes UV and a majority of colors, save red. Beyond this, there are three additional eyes specially designed to discern polarized light.

Yet, the bumblebee’s sense of smell steals the show. It’s about a hundred times more sensitive than ours, capable of detecting illegal drugs or explosives at airports. It can even recognize early signs of pregnancies, cancers, or diabetes.

What the scientists learned about bumblebee smell

Now, scientists have revealed another extraordinary capability in these buzzing creatures – bumblebees use their exceptional sense of smell to locate their nests, particularly when the landscape suddenly changes. This latest revelation is reported in Frontiers in Behavioral Neuroscience.

Sonja Eckel, a PhD student at the Department of Neurobiology of Bielefeld University in Germany, who is the first author of this research, explained, “Here we show that bumblebees rely on their own scent marks, which they deposit at their nest entrance while leaving for a foraging trip, to find back home when the visual cues are not sufficiently reliable.”

How the bumblebee smell study was conducted

In order to learn more about bumblebee smell, Eckel and her team observed the homing behavior of buff-tailed bumblebee (Bombus terrestris) in the laboratory. In the wild, these bumblebees nest in vacant mouseholes, concealed beneath grass or leaves. In the lab, the bees were trained to identify their nest entrance using two sets of visual cues inside a circular, enclosed flight arena.

The first set of cues included three black vertical stripes, each measuring 12cm wide and 85cm long, contrasted against the white walls of the arena. The second set comprised three cylinders, each 2.5cm wide and 15cm high, arranged in a triangle around the entrance hole.

The arena floor offered no visual cues. It featured a chaotic red-and-white pattern that appeared as black and white to the bumblebees. Following some training, the worker bees navigated directly to the entrance after trips to an outer chamber where they had been provided with nectar and pollen.

Focusing on bumblebees’ scent glands

Bumblebees are covered in several scent glands, which leave a chemical trace whenever they touch any surface, including their nest entrance. The researchers captured these scent marks by placing a glass ring around the entrance, which the foragers inevitably crossed when entering or exiting the nest.

The scientists then deceived the bees, shifting both sets of visual landmarks suddenly and independently. The landmarks now indicated false locations of the entrance. The real entrance was concealed, and none of the returning foragers could locate it.

Based on the conflicting landmarks, the researchers measured the time and distance at which the returning foragers hovered around either false location for the entrance. If a forager lingered around a spot for a longer duration and flew at a shorter average distance from it, she was considered more focused on that spot as the likely location of the entrance.

Typically, foragers seemed equally focused on either false location, indicating they relied on both sets of visual landmarks to fruitlessly try and locate their nest. However, when the researchers placed the glass ring with bumblebee scent marks around either location, foragers overwhelmingly concentrated on the false location suggested by the scent marks, hinting that bumblebee smell was guiding them.

Bumblebees have a backup plan if they get lost

The researchers concluded that bumblebee foragers utilize both their sense of smell and vision to find their way back home, particularly when visual information is conflicting.

“While visual information is perceived over larger distances and leads a bumblebee towards the approximate location of the nest, scent marks are used to pinpoint the exact location of the nest entrance in the near range. Most likely, physical contact is necessary to identify the scent,” explained Eckel.

“Our chemical analysis showed that this scent is a bouquet of hydrocarbons, fatty acids, and other substances, such as esters and alcohols. Many of these substances are known to be used by bumblebees in other behavioral contexts, also by other insect species.”

Next step: learning how bumblebees combine their senses

Eckel and her team are eager to carry forward this research. They aim to study how bumblebees learn and combine different sensory cues. The objective is to understand how these creatures distinguish between various behaviorally relevant targets, such as the nest hole and food sources.

Eckel’s research breaks new ground in our understanding of bumblebees, providing exciting insights into their navigational strategies. More than just charming garden visitors, bumblebees prove to be complex creatures, masterfully navigating their world using a combination of visual cues and scent marks.

This deep dive into the fascinating world of bumblebees and the way that bumblebees smell offers not only a greater appreciation for these humble insects but also potential inspiration for new technological applications. 

From drug detection to aiding in medical diagnoses, understanding the bumblebee’s sense of smell could hold significant implications for many fields of study. And who knows what further secrets these buzzing navigators of the insect world might yet reveal?

More about bumblebees

Bumblebees, belonging to the genus Bombus within the bee family Apidae, are robust and large-bodied insects known for their distinctive buzzing sound and important role in the environment. Here are some key aspects about bumblebees:

Physical characteristics

Bumblebees are larger and rounder than many other bee species. They’re generally characterized by their black and yellow body hairs, often in bands, although some species have orange or red on their bodies, or may be entirely black.

Habitat and range 

Bumblebees are native to almost every continent on Earth, but they are most common in temperate climates. They are versatile and can be found in a wide range of habitats, including forests, meadows, gardens, and even in the high arctic tundra.

Social structure 

Bumblebees live in colonies typically consisting of a single queen and worker bees. The queen is the mother of all bees in the colony. The workers, which are all female, perform various tasks such as foraging for food (pollen and nectar), feeding the young, and defending the hive.

Life cycle 

The life cycle of a bumblebee colony begins in the spring when a queen, who has overwintered and survived in a safe place, emerges and finds a suitable location for her nest. She starts the colony by laying eggs that were fertilized the previous year. 

The larvae that hatch are fed by the queen and eventually develop into worker bees. The workers then take over the task of foraging and caring for the new larvae, allowing the queen to focus on laying more eggs. As summer ends, the queen lays some eggs that develop into males and new queens. These leave the nest to mate, and the cycle continues.

Role in the ecosystem 

Bumblebees are vital pollinators, meaning they help plants reproduce. When a bumblebee lands on a flower to gather nectar, pollen from the flower sticks to the hairs on the bee’s body. When the bee lands on the next flower, some of this pollen rubs off, pollinating the flower. Many plants, including several crops, depend on this process for fertilization.

Unique characteristics 

Bumblebees are capable of a process known as buzz pollination, in which the bee grabs onto a flower’s stamen and vibrates its flight muscles rapidly. This vibration dislodges pollen that would otherwise have remained trapped.

Sensory abilities and bumblebee smell

Bumblebees have an excellent sense of smell and vision. They can distinguish UV light and most colors except red. They also rely on their sense of smell to locate their nest and even recognize early signs of pregnancies, cancers, or diabetes, as research shows.

Threats

Bumblebee populations are facing significant decline worldwide due to factors like habitat loss, climate change, pesticide exposure, and diseases. This is a concern not only because of their ecological importance as pollinators but also because of their role in supporting wild flora and agricultural systems.

Conservation 

Conservation efforts for bumblebees focus on preserving their natural habitats, reducing the use of harmful pesticides, and promoting practices that support their populations, like planting native flowering plants.

These are some of the key aspects about bumblebees. They are truly fascinating creatures, playing a crucial role in our natural world.

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