Ask the Naturalist

Ask The Naturalist: Why Do Honeybees Clean Themselves?

July 30, 2015

I was sitting in my car this afternoon when I noticed a cute little bee on my windshield appearing to desperately clean something off itself. At first I thought, oh no, it fell into something and now it’s going to die from whatever contaminated it. I took a cup and put the bee inside, but it rebelled and flew out. When I returned home I googled it and learned that bees do this — clean off pollen, etc. — and especially their eyes before flying home to their hives! Why do bees clean themselves?

The inside of a bee hive is considered to be a pretty clean environment. The bees produce honey there and we eat it. But, why are honey bees and their hive so clean? It is in their genes.

Honey bees are akin to animated robots that move around in their environment responding to stimuli with behaviors that have served them well for millions of years. Building wax combs to use for food storage and baby bee production allows the bees to keep tens of thousands of bees huddled close together. However, if any type of microbial outbreak occurs, all this closeness could lead to an epidemic and colony death.

The dwarf honeybee in various stages of development. Photo: Vipin Baliga/Flickr
The dwarf honeybee in various stages of development. Photo: Vipin Baliga/Flickr

The bees exhibit a behavior that deals with that problem. They collect resins from various plant sources. They return to the hive with these sticky masses where their sisters help to unload them. Beekeepers call this substance bee glue (propolis) because it is used to fill small cracks in the hive and cements the boxes together. It also is mixed with beeswax and used as a thin varnish to line the walls of the hives and sometimes portion of combs. Those resins have surprising antimicrobial properties that are effective against bacteria, fungi, and viruses. So, the bees are encased in a shell of antibiotics. Some have suggested that the inside of a hive is as clean as a hospital room, but we are not quite sure about that.

As for the bees themselves, it is common to see them using their legs or mouthparts to clean off other parts of their bodies. For bees, we might think that they are simply moving around or brushing off pollen that they picked up when foraging. However, honey bees live in a suit of armor called an exoskeleton. The exoskeleton is waterproof and protects the insects from invasive microbes. But bees also have to sense what is going on around them, so they have sensory receptors on the surface of their exoskeleton. The most obvious sensory organs on bees are their compound eyes. Honey bees can see objects, detect polarized sunlight, and have good color discrimination, similar to that of humans, but shifted a bit in the color spectrum. Bees wipe their eyes every so often to keep them clean. We humans have eye lids that keep our eyes clean and moist.

The rest of the sensory organs on the exoskeleton are sensilla (stiff hairs and protuberances) or pits that serve as sensory receptors. The tips of honey bees’ antennae have many touch receptors, odor receptors, and a special sensory organ called Johnston’s organ that tells them how fast they are flying. Other sensilla bend when the bee changes positions, so it remains aligned with gravity when it is building comb cells. Sensilla on a queen bee’s antennae help her determine the size of a comb cell, which determines if she lays a worker- or drone-destined egg. So, all those sensilla must remain dust and pollen-free to function properly, allowing bees to remain as busy as, well, bees.

About the Authors

Eric Mussen is an entomologist at the Honey Bee Research Facility at UC Davis.

Elina Nino is an apiculturist at the UC Extension.

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