By Emily Dennis, @emilyjanedennis
Bees are cool.
In the early 1900s, researchers like the tremendous Karl von Frisch noticed that when a group of bees gets too big, the queen will lay eggs and then leave the hive, bringing with her 10,000 of the worker bees. These bees swarm on a branch for several hours, or even days. Then, they all fly off at the same time and head toward their new home. Until 2010, the way the bees make this collective decision was a mystery.
Recently, we discovered that the swarm sends out scouts to collect information and then ‘debate’ about which site is best. At the end of this process, they all agree on one site and then fly there to build their new home.
When I first heard about this, I wanted to know how scientists figured it out. It’s really difficult to do experiments with bees because they need miles of space to fly around. To get around this problem, the research team, led by Dr. Thomas Seeley, did their experiments on an island that didn’t have any good natural homes for the bees. This allowed them to set up artificial bee homes of different qualities and in different locations around the island. Each artificial bee home was color coded and assigned a researcher, armed with some paint and a paintbrush. When a bee visited one of the artificial homes, the experimenter painted the bee with a small, colored dot representing the home they just visited.
Lucky for us, they also recorded everything with video cameras.
Seeley and his team observed that a few scout bees left the swarm to look for a new home. Once a scout found one of the artificial homes, she explored it and flew back to the hive. At this point, she needed a way to tell the other bees about the candidate’s location, distance, and quality. She did this using a ‘waggle’ dance:
In this video, you can see the bee with the blue dot telling the other bees about the cool candidate home she found. She dances in circles, interrupted by long ‘waggles’ in a pattern that looks like this:
The length and angle of the diagonal waggle part of the dance tells the other bees the distance and direction of the new potential home. In addition to location, the bees also need to convey the quality of the new site. Although researchers are still doing experiments to figure out exactly how the bees communicate this quality information, they did notice that if a bee finds a really good quality home, she will dance, on average, many more times in a row than if she found a place that was just good enough.
At any given time, a bunch of scouts are performing this behavior: leaving the swarm, investigating new homes, and then returning to the swarm to dance about them. If this was the end of the story, the bees would never make a single, swarm decision. Somehow, they need to choose between dances and settle on the best site. As an integral part of this decision-making process, if one dancing scout sees another scout do a different dance, she will try to make her stop by headbutting the dancer while making a noise:
The blue/yellow bee is being headbutted by the pink bee.
Once the blue/yellow bee stops dancing, she’ll watch another bee’s dance, check out that bee’s recommended home, and will then return to the hive, and start dancing about the new home. The research team also noticed that if a bee is dancing about a really great home, it may take more headbutts to get her to stop dancing.
Over time, the number of bees doing a dance for the best location slowly increases and more bees leave to check out this new home. At some point, the number of bees leaving the hive to check out this home gets pretty high. We’re still not totally sure how, but when there are ~15 bees outside a potential home site, this information reaches the hive and soon the whole swarm lifts up and moves into this new, ‘democratically’ chosen home. Like this:
In the future, these researchers hope to figure out:
- How do the swarms ‘know’ that there are 15 bees at a new location?
- How do head butts stop individual dancing bees?
- How do the bees use neurons to translate the length of the dance to distance?
- What makes a scout bee different from the other thousands of bees that don’t scout?
Bees have been everywhere in the news lately! Check out these (lay-friendly) articles to learn more about recent bee research
- caffeine may help bees remember things original research here
- bumblebees can be trained to respond to changes in a flower’s electric field! original research here
- have you heard scary stuff about ‘colony collapse’? If you want to learn more, this is a good summary of the problem and what’s being done about it.