Bumblebees Use Scent Marks to Navigate Home

Summary: Bumblebees utilize their highly sensitive sense of smell to locate their nests, particularly in conditions where visual cues are unreliable.

In experiments, scent marks left by bumblebees at their nest entrance helped them return home when visual landmarks were altered. This new insight highlights the multisensory navigation capabilities of these pollinators.

The findings could inform future research on how different sensory cues are learned and combined by bumblebees for essential behaviors.

Key Facts:

  1. Bumblebees have been found to use their own scent marks, left at the nest entrance, to find their way back home, especially when visual cues are unreliable or altered.
  2. Bumblebees’ sense of smell, about 100 times more sensitive than humans’, allows them to identify these scent marks, which consist of a bouquet of hydrocarbons, fatty acids, and other substances.
  3. The scent marks are passively left on surfaces the bumblebees touch, such as the entrance to their nest.

Source: Frontiers

Put yourself in the exoskeleton of a bumblebee for a moment: your world would be a riot of colors and scents, both essential to guide your search for pollen and nectar.

Bumblebees have excellent vision: they have a pair of compound eyes that can distinguish UV and most colors except red, plus three additional simple eyes specialized in detecting polarized light.

This shows a bee.
Bumblebees possess multiple scent glands, which distribute chemicals all over their body. Credit: Neuroscience News

Their sense of smell dwarfs ours: approximately 100 times more sensitive, and capable of sniffing out illegal drugs or explosives at airports, confirming pregnancy in women, or detecting cancers and diabetes in early-stage patients.

Now, researchers have shown that bumblebees can also use their sense of smell to locate their nest. This is especially important when the landscape suddenly changes, for example when familiar visual landmarks are blown away by wind.

The results are published in Frontiers in Behavioral Neuroscience.

“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,” said first author Sonja Eckel, a PhD student at the Department of Neurobiology of Bielefeld University in Germany.

Visual landmarks

Eckel and colleagues studied the homing behavior of the buff-tailed bumblebee Bombus terrestris in the laboratory. In nature, these bumblebees nest in abandoned mouseholes, hidden under grass or leaves.

Here, the foragers had learned to locate their nest entrance by visually orienting themselves against two sets of landmarks within a round enclosed flight arena, 150cm across and 85cm high.

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

The arena floor provided no visual information, being covered with a random red-and-white pattern – presenting as black and white for bumblebees.

After some practice, workers flew straight back to the entrance when returning from a visit to the outer foraging chamber, where they were provided with pollen and nectar.

Bumblebees possess multiple scent glands, which distribute chemicals all over their body. Previous research has shown that whenever they touch any surface, for example that of their nest entrance, they passively leave scent marks.

The researchers captured these scent marks by placing a glass ring around the entrance, which foragers tended to walk across when exiting or returning to the nest.

Tricking the bumblebees

Eckel et al. then tricked the bumblebees by abruptly changing the location of both sets of visual landmarks, independently of each other. Now, these gave conflicting information about the entrance’s location, neither marking the correct spot. The true entrance was closed off and concealed – with success, as none of the returning foragers subsequently found it.

The researchers measured how long, and at which distance, returning foragers hovered around either false location for the entrance, based on the conflicting landmarks. They assumed that the longer a forager hovered around any spot, and the smaller her average flight distance to it, the more focused she was in that spot as the best candidate for the entrance’s location.

Typically, foragers seemed equally focused on either false location, implying that they used both sets of visual landmarks to unsuccessfully try and relocate their nest. But a dramatic change occurred whenever the researchers placed the glass ring – carrying bumblebee scent marks – around either location. Now, foragers overwhelmingly focused on the false location suggested by the scent marks.

The researchers concluded that foragers use their sense of smell as well as vision to find their way home, in particular when visual information is conflicting.

Bouquet of scents

“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,” said 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.”

“In our follow-up research, we want to investigate how different sensory cues are learnt and combined by bumblebees to allow them to discriminate different behaviorally relevant goals, such as the nest hole and food sources.”

About this neuroscience research news

Author: Mischa Dijkstra
Source: Frontiers
Contact: Mischa Dijkstra – Frontiers
Image: The image is credited to Neuroscience News

Original Research: Open access.
Nest-associated scent marks help bumblebees localizing their nest in visually ambiguous situations” by Sonja Eckel et al. Frontiers in Behavioral Neuroscience


Nest-associated scent marks help bumblebees localizing their nest in visually ambiguous situations

Social insects such as ants and bees are excellent navigators. To manage their daily routines bumblebees, as an example, must learn multiple locations in their environment, like flower patches and their nest.

While navigating from one location to another, they mainly rely on vision. Although the environment in which bumblebees live, be it a meadow or a garden, is visually stable overall, it may be prone to changes such as moving shadows or the displacement of an object in the scenery.

Therefore, bees might not solely rely on visual cues, but use additional sources of information, forming a multimodal guidance system to ensure their return home to their nest.

Here we show that the home-finding behavior of bumblebees, when confronted with a visually ambiguous scenario, is strongly influenced by natural scent marks they deposit at the inconspicuous nest hole when leaving their nest.

Bumblebees search for a longer time and target their search with precision at potential nest locations that are visually familiar, if also marked with their natural scent.

This finding sheds light on the crucial role of odor in helping bees find their way back to their inconspicuous nest.

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