By This week is Pollinator Week! To celebrate I thought I’d feature a really cool research study on personality in honey bees. I’ve also added a Q&A with one of the scientists behind the research. Let’s dive in!
The word “personality” in the title of the research paper caught my eye. It’s not a word often associated with bees, because it may seem like honey bees are just little robots doing their chores. After all, there are tens of thousands of honey bees in a honey bee hive, and lots of work needs to be done to keep the hive clean, to feed everyone, and to make sure all of the baby bees grow into strong adults. The bees split up the labour: younger bees feed the larvae (baby bees) and do “housekeeping” chores, whereas older bees tend to guard the nest and go outside to collect food (pollen and nectar). The entire colony is a well-oiled machine, with every bee doing her part. Could there be any room for honey bees to show individual differences?
Bumble bee colonies are quite similar, in that there are housekeeping bees and food-gatherers and even undertaker bees. During my many hours of watching bumble bees when I was in university, I could often tell bees apart based on what I liked to think of as their “personality.” Each bee had a numbered, coloured, plastic disc that I had glued to their back so I could tell them apart. But each bee behaved a little differently. For instance, Green#6 was always hopping at the door to get out and start foraging (yes, she actually jumped up and down). Yellow#2 was always a little slow to start but once she began foraging she was a little workhorse. And Red#10 always flew around our flight cage for a little while before landing on a flower, instead of just flying straight to a blossom like the other foragers. I wondered whether bees actually did have their own little personalities. And how would we determine that scientifically? Turns out I wasn’t the only scientist who wondered about this.
I am also excited to feature this particular research article because one of the authors is Dr. Amy Toth, who I feature in my upcoming book, The Beekeepers. She does amazing research on honey bees, bumble bees, and wasps. The other author is Dr. Alexander Walton, who very kindly chatted with me about their experiments and what it was like working with the bees (more on this soon).
So, first off, what do Drs. Walton and Toth mean when they talk about “personality”? They think of personality as having three parts. One is consistency over time: a bee acts in a specific way throughout its life. Another is that no matter what situation the bee finds herself in, she behaves in a similar way. This is called consistency over contexts. And finally, the individual shows consistent, related clusters of behaviours. Somehow Drs. Walton and Toth had to test for these three things in honeybees. How did they do it?
Drs. Walton and Toth designed two experiments. In the first experiment, they placed small groups of newly-hatched honey bees into small Plexiglas cages. This allowed them to watch their behaviour much more easily (remember: there are thousands of honey bees in a hive!). On each bee they glued a coloured, numbered plastic tag to the thorax (the bee’s back or middle section).
In their first experiment, Drs. Walton and Toth presented the bees with three different situations and watched how the bees reacted. These situations were based on natural events that the honey bees would experience in their hive. One situation was presenting the bees a microscope slide that had queen mandibular pheromone smeared on it. Queen mandibular pheromone is a chemical that the queen bee gives off when she wants to be fed, and it causes worker bees to touch the queen with their antennae and feed her with their proboscis (tongue). (You can buy synthetic queen mandibular pheromone. I had no idea!)
Another situation was presenting the bees a microscope slide with honey bee alarm pheromone smeared on it. They got alarm pheromone from crushed bee stingers and venom sacs. Alarm pheromone is a chemical that guard bees give off when the hive is being attacked, and it causes worker bees to assemble and help defend the hive.
Finally, Drs. Walton and Toth presented the caged bees with an intruder bee from another colony. They actually tied a piece of fishing line around the middle of a honey bee, placed her in the cage, and then after the caged bees reacted, they pulled the harnessed bee out. Pretty clever! (They chilled the intruder bees a bit to slow them down so that they could tie the fishing line around them. The bee then woke up after they were tied. They did the same thing when labelling the bees: they chilled them for a bit first so they would be still during the labelling process. They bees eventually woke up and went back to normal.)
So, in each of the small cages, newly-hatched honey bees were presented with three things to react to: (1) a chemical signal that said, The queen is hungry! Feed her! (2) a chemical signal that said, The hive is under attack! and (3) an actual stranger honey bee invading the cage. Remember that to show personality, the caged bees would have to react similarly over time and across all three situations. Drs. Walton and Toth presented these three situations to the caged bees multiple times over 17 days. (That was how long the bees lived for before they died. Honey bee works have relatively short lives!) What kinds of behaviours did Drs. Walton and Toth look for? They wrote down whether the caged bees did any of the following: trophallaxing with a cage-mate (exchanging food tongue-to-tongue); attacking a cage-mate; using their antennae to touch the microscope slide with queen mandibular pheromone; using their antennae to touch the microscope slide with alarm pheromone; attacking the intruder bee. In all, they had 35 small cages with 171 honey bees to watch. What did they find?
For the first dimension of personality, that bees needed to show similar behaviour over time, they found that yes, honey bees tended to repeat their behaviour over the 17 days of the experiment. Hooray! The first requirement of personality was met!
For the second dimension of personality, that bees needed to show similar behaviours across different situations, they found evidence for this, too! Caged honey bees that were aggressive toward a cage mate when presented with a microscope slide with alarm pheromone were more likely to be aggressive toward cage mates when in the presence of queen mandibular pheromone as well. In other words, some caged honey bees seemed to have a more aggressive personality compared to other caged bees. Also, caged bees that showed trophallaxis as a reaction to queen mandibular pheromone were more likely to show trophallaxis in the other two contexts as well (that is, alarm pheromone and intruder). Trophallaxis is thought to be used not only to feed other bees, but also to exchange queen and forager pheromones, to inform other bees about the food needs of the colony, and to exchange information about the quality of nectar a forager collected. So maybe bees that show trophallaxis across situations have a “communicator” personality?
Now for the second experiment. For this one, Drs. Walton and Toth focused on the third part of personality: behaviours that tend to cluster together. After they noticed that some caged bees showed trophallaxis across situations, they wondered whether some honey bees are more “interactive” with other bees. So, they figured out a list of behaviours that bees would need to show to be considered “interactive bees”:
- Grooming other bees
- Caring for baby bees
- Waggle dancing
- Following another bee who is waggle dancing
- Guarding the hive
- Feeding the queen or touching her with their antennae
- Trophallaxis
They distinguished interactive bees from “non-interactive” bees. Non-interactive bees were bees that spent most of their time:
- Cleaning cells in the hive
- Fanning their wings to help keep the temperature steady in the hive
- Going outside of the hive to forage for nectar
- Going outside of the hive to forage for pollen
- Processing pollen
- Processing nectar
- Grooming themselves
- Washboarding: scraping her legs and mouthparts across wooden surfaces of the hive (we’re not sure why they do this…)
- Working the wax in the hive
This time, instead of watching small groups of honey bees in tiny cages, Drs. Walton and Toth watched bees in a full colony, so they could look for all of the behaviours that are listed above. They had special hives built that had Plexiglas walls so they could watch the bees without disturbing them. They labelled and watched over 1000 honey bees in 4 Plexiglas hives. That’s a lot of bees to watch! This experiment was a biggie.
After many, many hours of watching the bees, was there evidence of clustering of interactive and non-interactive behaviours? Although honey bees did not show a perfect distinction between interactive and non-interactive behaviours (that is, individual bees sometimes showed both), non-interactive behaviours tended to cluster together. The strongest relationship was between washboarding and wax work: honey bees that performed one of these behaviours tended to perform the other as well. Even though Drs. Walton and Toth spent oodles of time watching over a thousand bees, more experiments will need to be done to give us a clearer idea about whether some bees are more interactive than others.
So, after all this work, did honey bees show evidence of personality? Yes, they did! Individual bees tended to show individual differences in their behaviour across time and different situations, and some honey bees were more non-interactive than others.
What I find so cool about this research is the clever methods used to investigate whether or not honey bees show evidence of personality. It is amazing to think that even though honey bees are “programmed” to switch tasks as they age, moving from inside-hive chores to more outside-hive chores, we now have evidence that they can still show individual differences as well. Like all good experiments, the ones featured here lead to more questions: What causes honey bees to differ in personality, as it is defined here? Why are some bees different from others? What benefit would different personalities be to bees and their survival? Do other insects show signs of personality?
I also had questions about what it was like to carry out these experiments, and Dr. Walton very kindly gave me answers!
Q&A with Dr. Alex Walton
Dana: What did you like doing most in this research study?
Alex: It is really rewarding to just sit and watch the inner workings of a hive of bees. There are so many individuals doing so many things, and so many bizarre behaviours. You constantly find yourself thinking, “Why is she doing that? What does that signal to that other bee?”
Dana: Were there any challenges in doing this research?
Alex: The study was very challenging because it required keeping track of hundreds of bees. I would slowly scan the observation hives from the top left to the bottom right, looking for marked bees and then writing down what behaviour they were performing. It was extremely tedious!
Dana: Can you talk a bit more about tying honey bees to fishing line? That must have been difficult!
Alex: The reason I tied them to the fishing line was so that I could easily retrieve them once the observation period was over. Trying to get a loose bee out of the cage (as she is being chased and attacked by other bees ) without accidentally letting any of the other bees out would not have been an easy task! I know from experience, as one of my tied bees did manage to wriggle free of her binding once in the cage and retrieving her was no easy task. However, tying a fishing line to a bee is no easy task either, as it really requires 2 hands (one to hold the bee down with forceps, and two to place the line around the bee and tighten). As I was not blessed with 3 hands, I would first chill the bee in the fridge to slow her down, then gently place a loop of fishing line around her waist.
Dana: Did anything about your results surprise you?
Alex: One of the main findings of the study is that honey bee workers have consistent behavioural differences throughout their lives. This was surprising because we know that honey bees have stereotyped behavioural transitions as they get older. They will switch from nursing tasks (feeding larvae, or baby bees) to outside tasks (foraging), and pretty much all of them do this. So, the fact that they still have distinct behavioural differences even as they shift behavioural repertoires was very surprising!
Dana: What advice do you have for kids who want to study bees or other animals?
Alex: Take some time (or a lot of time) to sit and watch animals: at a bird feeder or bird bath, follow a trail of ants to their anthill, watch the squirrels at the park interact with each other. Then, start asking yourself questions about what you observe, and write those questions in a notebook (it isn’t real science unless you write it down!): Why is that bird splashing around in the water? Why are those ants attacking that other ant? Are those squirrels playing or fighting? Try to come up with your own explanations for your questions, and then fact-check them by looking online or in a book. The first skills a scientist needs to develop are a keen eye for observing nature and an inquisitive mind that is always asking questions. For kids who want to study bees in particular: 1) go to a flower patch and watch the bees visiting flowers. See if you can follow one bee’s path: how many flowers does she visit? Are they all the same kind? 2) Visit with a beekeeper who will open up a hive and show you what the bee home life is like, and 3) Don’t be afraid to get stung! Yes, getting stung is not fun but it’s not the most painful thing in the world. For every bee scientist, the first thing they had to do was get confident around bees.
Dana: What are you studying now?
Alex: Currently, I am studying the evolution of cooperative behaviour in paper wasps.
That sounds like a great topic for a future blog post! Happy Pollinator Week!
Reference
Walton, A., & Toth, A. L. (2016). Variation in individual worker honey bee behavior shows hallmarks of personality. Behavioral Ecology & Sociobiology, 70, 999-1010. DOI: 10.1007/s00265-016-2084-4