Washboarding is a rhythmic behavior observed in honey bee colonies, most commonly the Western honey bee, Apis mellifera. It involves dozens to hundreds of worker bees moving in a synchronized, rocking motion on the surface of their hive. Despite decades of observation, the exact function of this collective activity remains one of the enduring mysteries in modern bee science. Researchers continue to propose several possible explanations for why bees engage in this seemingly purposeful task.
Defining the Washboarding Action
Washboarding is a distinctive action where worker bees position themselves on the hive surface, often in neat, discernible rows. Each bee anchors itself primarily using its middle and hind legs, while the front two legs and the head perform the action. The bee then engages in a rhythmic, side-to-side rocking motion, appearing to scrub the substrate beneath it.
During this motion, the bee repeatedly grasps the surface with its mandibles and scrapes or strokes the area with its forelegs. This behavior is reminiscent of scrubbing clothes on an old-fashioned washboard, which is how it earned its name. The action typically takes place on the hive’s outer landing board, near the entrance, or on the inner surfaces of the hive boxes.
The behavior is performed by house bees, typically those between 10 and 25 days old, before they transition to foraging. This synchronized movement often creates a faint scratching sound, and observers have noted that bees sometimes appear to lick the surface as they rock. The combination of rocking, scraping, and mandibular contact suggests a task focused intently on the immediate surface area.
Primary Scientific Hypotheses
The most widely discussed hypothesis posits that washboarding is a form of surface cleaning and sanitation. Researchers observe that the repetitive scraping motion may serve to remove debris, polish surfaces, and eliminate rough spots where pathogenic organisms might gather. The meticulous nature of the behavior, focused on the common entrance area, suggests an effort to maintain a clean and healthy environment for the colony.
Another theory suggests the behavior is related to communication through the distribution of chemical signals. The rhythmic motion may help spread colony-specific pheromones, such as those from the tarsal or Nasonov glands, onto the hive surface. This deposition of scent could reinforce the colony’s unique olfactory signature, aiding returning foragers in orienting and identifying their home.
A third explanation focuses on the bee’s internal needs rather than an external function, proposing that washboarding is a form of physical conditioning or a means of occupying idle workers. This theory suggests the rocking and stroking motions could strengthen thoracic muscles and reinforce neural pathways necessary for complex tasks, such as wax building. Conversely, it has also been viewed as non-adaptive “busy work” for young house bees who have no immediate tasks during periods of low nectar flow.
Environmental Context and Frequency
Washboarding is influenced by external conditions, most frequently occurring during the warmer months when the colony is highly active. The activity is typically observed when temperatures range between 70°F and 85°F, and is common during humid or lightly overcast weather. The frequency of the behavior tends to increase from the morning, often peaking in the early to mid-afternoon, and continuing until early evening.
The surface material on which the bees are working plays a role in the intensity of the behavior. Studies show that washboarding is more prevalent on rougher substrates, such as unpainted wood or slate, compared to smoother materials like glass or plastic. This preference for textured surfaces supports the hypothesis that the bees are physically scraping or polishing the area.
The behavior’s correlation with the colony’s internal state is varied. It has been noted during times of heavy nectar flow, when high traffic requires constant maintenance, and also during periods of nectar dearth, when bees may be idle. The presence of washboarding is not universal across all colonies, even those in the same location, suggesting that a genetic component may influence the behavior.