A study on the grooming habits of bees has given new physical insight into the process of pollination, and could have implications for future MEMS. Researchers from the Georgia Institute of Technology in Atlanta, USA, and Kiel University in Germany, examined how pollenating insects that purposely cover themselves with millions of pollen particles get clean enough to fly. Their study, published in the journal Bioinspriation and Biomimetics, found that the key lies in the tiny hairs bees and other pollinators are covered in.
They also found that the viscous fluid on the surface of pollen grains (or pollenkitt) plays an essential role in the process, by helping the pollen stick to the insect. Co-author Professor David Hu from Georgia Tech said:
“When it visits flowers over the course of a day, a typical worker bee can pick up five times its body weight in pollen on the hairs on its body. Of course, being completely covered in pollen particles will make sensing and controlling flight difficult.
“So how do the bees get themselves clean? We found their hairiness is the key not only to collecting the pollen but to getting clean as well. The hairs on the bees’ eyes, for example, are spaced so they suspend the pollen above the body, so it can be easily removed by the forelegs. In turn, the spacing of the hairs on the foreleg dictates the leg’s capacity to store pollen, and the amount it can remove with each swipe.”
The researchers developed an experiment to quantify the grooming performance of bees. They used a live honey bee coated in pollen and two cameras – one to film the bee’s cleaning motions, and the other to capture silhouettes of the pollen particles as they fell into a dish – to record the number of swipes the bee made to clean itself, and how much pollen it removed. They also looked at the motion the bees used, and the geometry and spacing of the hairs.
The team used two different types of pollen – commercially available bee pollen, and dandelion pollen – as well as corn starch to examine whether the size or type of the pollen grains made a difference to the rate of cleaning. By washing some of the pollen, they tested whether pollenkitt increased the pollen’s adhesive properties.
Professor Hu said: “Grain size has a major effect on whether pollen can be removed. We found bees could easily clean off around 15,000 particles of commercial pollen in three minutes, whereas they were still covered in corn starch after three minutes, as the grains are much smaller.
“We also found the presence of pollenkitt plays an important role in pollen accumulation. Honeybees accumulated half as many pollen grains when the pollenkitt was removed. We believe this study is the first to provide physical insight into the critical process of pollination."
The team found that pollen type or initial pollen accumulation has no effect on grooming behaviour. However, they identified that the geometry of the hair on both the surface to be cleaned, and the one that does the cleaning, dictated their efficiency.
The hair spacing on the bee’s body is tuned to the particles they collect, to allow suspension and easy removal, while hair spacing on the grooming legs allows the transfer of particles from the body to the legs and determines the amount of pollen removed during each swipe.
Professor Hu said: “Furthermore, the methods used by pollinating insects for accumulating and removing micro-scale particles could influence designs for cleaning human-made surfaces, and generate brush-based surfaces with filtering and/or particle separating properties. With the emergence and growth of microelectromechanical systems, there are definitive implications for effective cleaning at the microscale.”