How Will I Get Home?

The story goes that a famous and absent-minded scientist, Norbert Wiener, left his new house in Boston so deep in thought that he gave no attention to where he was. Unsurprisingly, at the end of his day in the lab he walked back to his old house instead. One thing that he had probably forgotten to do on leaving in the morning was to turn around and memorise what his new house and its neighbors looked like, so he could find it again. This home-finding process is important for insects as well. Insects that have nests and forage for food that they bring home to feed their young know instinctively what they must do the first few times that they leave their nest. It is to turn around and face their nest and learn the appearance of its surroundings.

The first well-known description of this behaviour was by a self-taught naturalist, Henry Bates, in the mid-1800s. He and his friend, A.R. Wallace, having never left England before, decided in their early 20s to go and observe animals and plants in the Amazon rainforest – a brave undertaking. Later, Bates describes the journey and his discoveries in his famous book ‘The Naturalist on the River Amazons’. In it he interprets the orientation flight of a wasp on leaving its nest: ‘The Bembix took note of the locality […] a mental act of the same nature that takes place in ourselves’. Bates had noticed the wasp’s ability to learn its nest location, by turning back to look at it, though he did not have instruments with which to record the behaviour that he saw. Video has now made it possible to study the details of this elaborate learning behaviour of insects.

The aim of our study was to understand an important feature of bumblebee ‘learning flights’ - the name for this behaviour. Bumblebees, on their first few departures from the nest, look back at it. While facing their nest, they also face in a single, preferred direction within their surroundings. The preferred direction may be a compass direction, like north, or a feature in the nest surroundings, like a nearby plant. This direction is in world-centered (geocentric) coordinates (see Image A). In contrast, the bumblebee could, in principle, face the nest from any direction. The coordinate of nest facing could be called egocentric, in the sense that it is related to the insect’s own body position when it is near the nest (see Image B). How then do bees coordinate these egocentric and geocentric directions so that, in their very first learning flight, they can look at a preferred feature while also facing their nest to remember how to get home? 

Image A: This shows a bee moving to coordinate geocentric and egocentric directions. Geocentric is when the bee faces (points its body) in a particular direction in its surroundings, here towards a cylinder. Egocentric is when the bee faces the nest (shown as a + symbol).

Image B: Three cylinders were placed on the table above the bee’s nest. The bee facing both the nest and the cylinder is considered to be coordinating egocentric and geocentric directions, respectively.

To find out, we studied the behaviour of bumblebee foragers when they left their nest and took their first view of the surroundings outside. Bumblebees tend to colonize deserted holes in the ground for their nest. Since it is difficult to do research with natural colonies, we buy ones that are commercially available. A colony comes conveniently in a cardboard box that we set up below a table with a hole in the center and gravel on top of the table to resemble natural ground with a nest entrance. A series of transparent tubes connects the nest to the top of the table so we can control each bee’s exit and entry. We call this the nest table. A new worker bee emerges ready to forage for nectar and pollen as it would normally do from a natural nest in the ground. A second table a few meters away has a feeder from which the bees can forage for sugar water that they take back to the nest. Both tables were in a greenhouse with three black cylinders arranged on top of the nest table, as indicated in Image B. Many of the bees emerging for the first time from the nest tended to face the same cylinder while simultaneously facing the nest. 

Bees are likely to face the nest through a process called path integration. Path integration is an important navigational strategy for many mammals, birds, and insects. It enables an animal to keep an updated record of its current distance and direction from its starting point, in this case its nest, so that at any moment, if it is scared or finds food, it can take a direct path back to the nest. 

Karl Von Frisch, who won a Nobel Prize for his work on honeybees, showed that bees perform path integration. He had earlier discovered that bees use a behaviour called the ‘waggle dance’ to signal to each other the direction and distance of a patch of flowers from the nest. Von Frisch then explored how bees signaled to other bees when a big and high obstacle, such as a mountain, separated a flower patch from the nest. Bees signaled that the flowers were to be reached directly through the mountain - the direct path, and the other bees would use this information to detour around the mountain to reach the flowers.

In the case of a learning flight, the starting point is the animal’s nest. To face the nest during a learning flight by means of path integration, a bee need only turn in that direction. Although bees could in principle face the nest from any direction, as shown in Image A, they generally chose to face the nest and their preferred cylinder at the same time. How exactly do they manage to reach this combination of egocentric and geocentric directions? 

We found that many bees adopted the same strategy. They pointed their body parallel to the direction of the preferred cylinder and flew sideways and perpendicular to that direction until they faced the nest (Image A). This strategy begs the question of how a bee at the start of its upwards scan knows the direction in which it should face. A possible answer is that, when bees are close to the nest and not necessarily facing the preferred cylinder, they learn the direction of the cylinder relative to the direction of the sun. 

The bee’s first return flight to the nest after foraging was also informative. Bees, when approaching the nest on their return, had a similar preferred viewing direction to that of their learning flight. This coincidence suggests that the bee does indeed memorise the view when it first faces the nest in its preferred viewing direction. This memorised view then determines the path that the returning bee should follow. Such a strategy is beneficial because during its learning flight the bee can pick out an advantageous direction from which to view and memorise the world. Such a direction would be one with enough detail in the surroundings to stop the bee from missing and overshooting the nest on its return.

Overall, our knowledge of learning flights has come a long way since their discovery by Henry Bates. This particular study shows us that bees use an intricate strategy to find their way to and from their nest. To do so, they perform an elaborate maneuver that requires them to have instinctive knowledge of properties of the external world and the ability to process multiple forms of information.

Written By: Dr. Thomas Collett & Dr. Natalie Hempel de Ibarra

Academic Editor: Engineer 

Non-Academic Editor: Fashion Designer 

Original Paper

• Title: How bumblebees coordinate path integration and body orientation at the start of their first learning flight

• Journal: Journal of Experimental Biology 

• Date Published: 12 April 2023

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