A bumblebee had pried open a lupine flower (Courtesy Photo / Kerry Howard)

A bumblebee had pried open a lupine flower (Courtesy Photo / Kerry Howard)

On the Trails: Social bees and social learning

Dancing, dialects and more.

Honeybees are very social insects, often living in large colonies under the aegis of a queen, who lays eggs that are tended by the worker-bees (all female). The workers forage for nectar and pollen in the area around the hive, bringing back food for the larvae. A successful forager often signals to her less-experienced nest-mates the location of a good food source (although other successful foragers may choose to continue with their own discoveries). The floral scent she carries stimulates her nest-mates to pay attention to the signals. Workers begin to forage soon after becoming adults, and then may start to follow a signaler as it signals; followers become better foragers than mere observers, but they don’t become signalers themselves until they have more experience.

If the food resource is close to the hive (tens of meters), the signals are presented as a circular route performed on the surface of the comb by the excited forager. But if the discovered food resource is farther away, the signals take the form of a “waggle dance.” The waggle dance conveys information about direction, distance, and quality of the resource. The dancer circles first one way and then the other, making a figure eight, doing the waggle of its abdomen while moving its feet (“running” but not going far) on the short straightaway between the adjacent circles. This pattern is repeated a number of times. The orientation of the dance on the comb (or “dance floor”) tells other bees the direction to go, the duration of the abdomen-wagging “run” on the straightaway tells distance, and the number of waggle runs tells about the quality of the resource. That basic story has been known for decades, but it turns out that there are also acoustic and air-flow signals from the dancer’s wing vibrations, about which much less seems to be known, and the dancers emit pheromones (perhaps stimulating recruits?). There may be tactile cues as well, occurring when a recruit follows a signaler closely enough to touch it with antennae. Some researchers call this a symbolic language.

That seems pretty straight-forward, and for species of honeybee that make their nests in the open, orientation by the sun is relatively simple — the dance is vertical if the direction is toward the sun, or it is oriented by the angle by which the resource deviates from the sun’s apparent location. But for honeybee species (such as the familiar western or domestic one) that nest in cavities, signaling orientation is a bit more complex. In these hives, the honeycomb is a vertical surface, and it’s dark in those cavities, no sun in sight. Somehow, these species have substituted gravity for sun-sights, but the angle of deviation from vertical still indicates the angle of deviation from the apparent direction of the sun. And furthermore, the bees are able to time-compensate for the lag between the dancing and the time of the next foraging expeditions, sometimes a matter of hours.

Experiments have shown that inexperienced bees that have teachers make fewer errors in their own dances than equally inexperienced bees not exposed to dancers. In short, not only do these bees learn from others about food resources, they also learn about how to communicate with each other — they are capable of what is called social learning, which means learning from teachers that actively pass on information.

The teacher-less bees learned to correct some of their own dance errors but never did learn to correct errors about distance, consistently over-estimated how far away the resource is. Some researchers suggest that such built-in error might actually be useful when the colony swarm to a new location and starts to explore the floral resources there.

Recognizing and integrating all that signaling information is a lot for a tiny brain (about one cubic millimeter in volume) to accomplish. But there’s more: the duration of the waggle run, the distance indicator, differs among types of honeybees, including different populations of the western/domestic species — there are “dialects” in the coding of the distance-indicator. When a population in general has short foraging range (resources are distributed close to the nests), the duration of the waggle run is shorter than when their foraging distances are longer, and different populations misinterpret each other’s signals if they are experimentally mixed. That is to say that these bees have culture—socially learned behaviors that are transmitted between generations across whole populations.

Bumblebees are social too, although they live in smaller colonies, usually a few hundred bees. The worker-bees forage for nectar and pollen to feed the larvae that the mother-queen produces. Foraging bumbles learn, by trial and error, how to exploit flowers of different shapes and arrangements of nectar glands and pollen-bearing stamens; they also learn how to open flowers that conceal their food rewards (such as snapdragons and monkshood). They tend to avoid previously visited flowers where other bees have left their scented footprints.

When a bumblebee worker has become proficient at exploiting certain flowers, she commonly tends to specialize on those flowers, seldom visiting those at which she is less efficient. These bees are capable of learning from each other by observation, as shown by laboratory experiments, but how often this occurs in wild bees has apparently not been recorded. They do use pheromones (airborne scent signals) to recruit their nest-mates to go foraging, and the recruits often start by sampling flowers with the aroma of the flowers visited by the successful forager. However, it seems that bumblebees do not actively teach each other about the location of floral resources, unlike honeybees. So, although bumblebees are very social, social learning may not occur in those species.

But why not? What is the critical difference between bumblebees and honeybees that led to the difference in teaching and social learning? Perhaps active teaching helps recruit the greater numbers of workers needed to feed a large colony? Or…?

• Mary F. Willson is a retired professor of ecology. “On The Trails” is a weekly column that appears every Wednesday.

A honeybee explores a thimbleberry flower (Courtesy Photo / Bob Armstrong)

A honeybee explores a thimbleberry flower (Courtesy Photo / Bob Armstrong)

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