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An evolutionary mystery: the taste and color of pollen

No one knows exactly when some of the ancient hunting wasps stopped chasing their meals and opted for veggies. We simply don’t have detailed records of early transitional species. What we do know is that some descendants of the early Crabronidae family of wasps gave up meat in favor of pollen, eventually becoming bees.

This article first appeared in American Bee Journal, Volume 159 No 2, February 2019, pp. 213-216.

By 80 million years ago, we had fully-formed social bees equipped with all the paraphernalia of modern pollen eaters. In fact, a bee preserved in New Jersey Cretaceous amber is a dead ringer for some of today’s stingless honey bees.1 Still, we don’t know when the changes occurred. In the typical way of evolution, the transition was probably a series of chance events that turned into something good for both bees and plants.

But how could it happen? Well, imagine this. Mama wasp goes hunting for food and pounces on a small beetle resting on an inconspicuous green flower. She zaps it with her stinger, then flies the helpless creature home to feed her young. But after she drops the insect in the nest, mama discovers something clinging to her thorax.

She tries to brush it away, but it transfers to her leg. She swipes it with another leg, but it sticks there, too. Like a piece of Velcro, a pollen grain adheres to everything it touches. Vexed, she finally drags her leg across the stunned beetle where it sticks like glue. Relieved to be rid of the thing, she mutters under her breath, “There, kid, eat that too.”

Agapostemon: An Agapostemon collects yellow pollen, the most common color. © Rusty Burlew.

The bee is born

Most likely, this scenario—or something like it—played out over and over until pollen became a regular part of the wasp diet. Maybe the offspring thrived on this food, or perhaps the mama wasp flourished because she no longer needed to tussle with so many unfriendly entrées. In any case, pollen most likely became part of the diet before it became the main event. Perhaps, over the millennia, pollen became a greater and greater portion of the menu: Pollen Medley. Pollen Glazed with Nectar. Pollen Primavera with Minced Beetle.

More hairs appeared on the insect’s body to help collect pollen, and later, the hairs became branched. Eventually, the descendants of the Crabronidae sported the complete pollen option—hairy bodies, antenna cleaners, electrostatic charges, pollen brushes, combs, and presses. They foraged in a world where the flowers had also changed. Newly evolved flowers had eye-catching colors, alluring odors, and sweet rewards. Suddenly—geologically speaking—these insects separated from their ancestors and the bee was born.

Nutritious pollen

If some wasps began eating pollen by accident, nutritious pollen must have already been available in the environment. Indeed, a recent finding of a beetle in ancient amber seems to support that idea.2

The fossilized beetle, Cretoparacucujus cycadophilus, was found preserved in amber along with pollen grains that appear to belong to an ancient cycad. Some evolutionary biologists believe that cycads were pollinated by beetles long before flowering plants appeared on Earth, perhaps as early as 250 million years ago.

The researchers reasoned that the preserved beetle was a cycad pollinator based on a number of clues. The proximity of pollen along with the shape of the mandibles, the presence of maxillary palps (mouthparts common in today’s pollinators), and the fact that modern descendants of the beetle still collect cycad pollen, all indicate an established relationship.

Since insects were consuming pollen long before wasps began using it as baby food, pollen was probably already quite nutritious. If beetle pollination was advantageous to cycads, cycad pollen most likely evolved to attract them. From there, the leap to other insect pollinators was almost inevitable.

Green pollen: A honey bee with green Ceanothus pollen.
Green pollen: A honey bee with green Ceanothus pollen. © Rusty Burlew.

A strange food

No matter how you look at it, pollen is on odd menu item. Pollen contains the male gametes of a plant. Of all the edible plant parts—leaves, stems, flowers, roots, fruits—it’s hard to imagine gametes being a hit. But in fact, pollen is a nutritional powerhouse, responsible for multiple lines of animal life and a complex web of plant/pollinator co-dependencies. A vast number of species eat pollen, and an incredible variety of pollen grains exist to feed them.

The diversity of pollen is even more mind-bending when you consider that many plants are pollinated by wind alone. Wind-borne pollen—the type that makes some folks wheeze and sneeze—is small and light, allowing it to travel for miles on soft currents of air. In comparison, animal-mediated pollen is often large and bulky and crammed with nutrients. While animal-friendly pollen is expensive for a plant to make, it has a much better chance of reaching its target than wind-blown pollen—a perfect example of nature’s economy.

In order to harvest the many types of pollen available to them, bees developed a panoply of pollen-collecting variations. Depending on what kind they collect, some bees have small hairs packed closely together, while others have long hairs spaced farther apart. Honey bees, stingless bees, and bumble bees carry pollen in moistened pellets, while most bees carry it in patches of hair located on their legs, abdomen, or thorax. Some bees swallow it whole and regurgitate it later, and many bees just steal it from other bees. Truly, it’s a zoo out there.

Blue pollen of scilla: This honey bee has collected a shiny pellet of blue pollen from Scilla siberica.Green pollen: A honey bee with green Ceanothus
Blue pollen of scilla: This honey bee has collected a shiny pellet of blue pollen from Scilla siberica. © Rusty Burlew.

Food that tastes good

Living creatures like food that tastes good. In fact, things that have gone bad or are dangerous to eat generally don’t taste all that great. Indeed, their foul taste warns us away. Since bees love nectar, honey, and syrup—all things that taste good to humans too, I assumed pollen must be tasty. So one day, I popped a few bee-collected pollen pellets in my mouth just to see. I cannot stress my discovery enough: Pollen tastes vile.

Afterwards, I heard that some pollen is worse than others, and I probably just tried an unfortunate sample. So I retained an open mind—at least until a few months later, when I was manning a honey booth at a local fair. I was serving little squares of comb honey on crackers when a gentleman at the next table gave me a piece of dark chocolate infused with pollen pellets, a confection he had purchased from another vendor.

Being an aficionado of dark chocolate, I was delighted, even though I was horrified at the price he’d paid. Since I didn’t know him, I especially appreciated the kind gesture. I eagerly peeled back the gold foil and took a bite.

Honestly, I didn’t know it was possible to desecrate a piece of chocolate to that degree. In fact, I didn’t know something could taste that bad without killing you. I immediately chased it with a mouthful of honeycomb and tried to choke the whole thing down while I graciously thanked the guy who was standing there watching me. If not, I would have spit.

Reasons for bitter

The question is simple: Considering that evolution created plants with sweet nectar, alluring oils, heavenly scents, and gorgeous colors, what’s with pollen? Must gametes be so gross?

My first thought was that bees may have a sensory spectrum different from our own. Just like they can’t see red, maybe they can’t taste vile. On the other hand, perhaps a more practical aspect is involved. Maybe plants don’t want bees to be too greedy for it. If it were overly delicious, the bees might not leave enough for pollination.

In a honey bee colony, the nurse bees are the primary consumers of pollen. They digest the pollen, which provides them with the nourishment they need to secrete brood food. Their glandular secretions are fed to the young larvae until they gradually transition to bee bread. Is it possible that fermented bee bread is tastier than freshly-caught pollen? Maybe. I have yet to try it.

In solitary bees the adults seldom eat pollen. Small mounds of pollen mixed with nectar are left for the larvae to eat without adult interference. So once again I wonder, does pollen mixed with nectar taste better than raw pellets? Certainly, chocolate doesn’t help. Making pollen attractive—but not too attractive—was probably an evolutionary strategy in the best interest of plants.

Bees on mariposa lily: A large Melissodes and two small Halictus (Seladonia) collect pink pollen on the Oregon high desert.
Bees on mariposa lily: A large Melissodes and two small Halictus (Seladonia) collect pink pollen on the Oregon high desert. © Rusty Burlew.

Sensing the flavor

Honey bees generally don’t taste pollen with their mouthparts until they eat the bee bread. Foragers that collect pollen stuff it into their pollen baskets, and later upload the pellets to the hive. However, they most likely do taste the pollen through the receptors on their antennae and feet. This seemed like a reasonable explanation for the bees’ tolerance to bitterness until some researchers found that honey bees do not detect bitterness with their antennal or tarsal sensors.3 Does that mean bitterness is not important to bees?

In my quest for an answer I found a paper entitled, “Bees found to use pollen’s taste to determine which flowers to visit.”4 The bees in this study were common eastern bumble bees, Bombus impatiens, and the pollen was purchased. In the experiments described, the bumble bees were offered pollen laced with powdered quinine, cellulose (control), or sucrose—all of which were presented on white artificial anthers.

Results showed the bees spent the most time collecting sucrose-laced pollen and the least time collecting quinine-laced pollen. When the bees were presented with different colored flowers placed close to the artificial anthers, the bees collecting quinine-laced pollen were the most likely to switch to a different color flower. The researchers speculated that the bees tasted the pollen when they groomed, so after grooming, bees were more likely to change flowers.

I finished the paper with more questions than answers. If bees don’t like bitter pollen, why is pollen bitter? Could the bees in the experiment be responding to quinine in particular rather than bitter in general? Clearly, more work needs to be done.

The structure of pollen

The pollen grain is designed to protect the plant’s male genetic material as it is transferred from one flower to another. In order to assure the genetic message is not scrambled in transport, or spoiled by bad weather, it is locked within several concentric layers.

  • In the center of the grain, the genetic package floats in a pool of cytoplasm. The cytoplasm acts like a cushion, but also provides the rich food source that bees require.
  • The cytoplasm is tucked inside a tough cellulose layer known as the intine.
  • The intine is wrapped in another layer called the exine. The exine, made of a substance known as sporopollenin, is designed to fend off environmental hazards like ultraviolet radiation, moisture, drying, changes in pressure, and fluctuations in pH.
  • Finally, the exine is coated with an extremely sticky substance called pollenkitt, which enables pollen to adhere to flowers without being blown or washed away. The stickiness also allows bees to clump it together in pellets. The odor, color, and taste of pollen also originate in the pollenkitt.

All these protective layers, especially the inner capsule of cellulose, make pollen extremely hard to digest. But bees can penetrate pollen’s weak spot—the germinal pore—with enzymes that allow them to digest most, if not all, of the grains. An examination of bee feces will reveal digested pollen grains that look like popped balloons. In those, everything is gone except for the tough cellulose husk. Some grains are only partially deflated, and some remain whole.

A colorful package

One of the first things beekeepers notice about pollen is its color. Pollen loads come in many shades of yellow, white, orange, pink, blue, gray, green and purple. The subtle variations in color often give us a clue as to where the bees foraged.

Because honey bees have flower fidelity, the pellets on their legs are a consistent color throughout. Other bee species, such as bumble bees, may have pellets layered with color like Neapolitan ice cream. I wondered, do bees care about the color of pollen, or is that delight reserved for humans?

Leafcutter on thistle: This leafcutter, Megachile (Sayapis), collected purplish-blue pollen from a thistle.
Leafcutter on thistle: This leafcutter, Megachile (Sayapis), collected purplish-blue pollen from a thistle. © Rusty Burlew.

Does the color matter?

We know that bees are attracted to flowers based on their scent and color, including ultraviolet patterns humans cannot see.5 We also know that bees scouting for food sources may bring home samples of nectar and pollen from flowers they visited.

But some scientists have concluded that honey bees are not good at determining the nutritional value of pollen, especially in the field.6 Honey bees have been known to collect sawdust and coffee grounds, for example, although these items apparently get the nix from nurse bees whose job it is to sort through the groceries. But if the odor or color of pollen were important to bees, why would they bring home such unappealing particles?

We know that the choice of pollen is sometimes made based on the physical characteristics of the flowers or the size of the pollen grains. Honey bees avoid pollinating alfalfa flowers because of the spring-loaded petals that bop them on the head. To collect alfalfa nectar, the bees go through the back of the flower where they touch no pollen. Honey bees also avoid plants like tomatoes, which require buzz pollinators to release the grains. In addition, honey bees often refuse to collect pollen that is too big and ungainly, such as hibiscus.7

No clue to color

After an extensive search, I have found no evidence that pollen color is a selection criterion for bees. One paper speculates that certain colors may make pollen especially visible to animal eyes (pollinators) or may hide pollen from other animal eyes (consumers), but the study was mostly conjecture and didn’t discuss bees in particular.8

Bees of all types make foraging decisions based on the color and scent of flowers. Once they get into a flower, it appears to be the sweetness of the nectar or the odor of the pollen that commands their attention. Perhaps the odor of pollen is much more compelling than either the color or the flavor—a situation that reminds me of coffee.

For now, the reasons for the gorgeous colors and bitter taste of pollen remain an evolutionary mystery. Personally, I will continue to admire and photograph bee-collected pollen, but I will pass on eating it in any form, regardless of how it’s disguised.

Rusty
Honey Bee Suite

References

  1. Michener CD, Grimaldi DA. 1988. The oldest fossil bee: Apoid history, evolutionary stasis, and antiquity of social behavior. Proceedings of the National Academy of Sciences of the United States of America, 85(17): 6424-6.
  2. Cai C. et al. 2018. Beetle pollination of cycads in the Mesozoic. Current Biology 28 (17): 2806-2812. https://doi.org/10.1016/j.cub.2018.06.036.
  3. De Brito Sanchez MG. 2011. Taste perception in honey bees. Chem Senses 36(8): 675-92. doi: 10.1093/chemse/bjr040
  4. Yirka, B. 2016. Bees found to use pollen’s taste to determine which flowers to visit. Phys.org. https://phys.org/news/2016-07-bees-pollens.html#jCp
  5. Muth F, Papa, DR, Leonard AS. 2015. Color learning when foraging for nectar and pollen: bees learn two colors at once. Published by the Royal Society. DOI: https://doi.org/10.1098/rsbl.2015.0628
  6. Permal SF, Currie RW. 2001. The influence of pollen quality on foraging behavior in honeybees (Apis mellifera) Behavioral Ecology and Sociobiology 51: 53-68.
  7. Mattingly R. 2012. Honey-Maker: How the Honey Bee Worker Does What She Does. Portland, Oregon. Beargrass Press.
  8. Pacini E, Hesse M. 2005. Pollenkitt – its composition, forms and functions. Flora 200: 399-415.
Multicolored pollen baskets: This bumble bee changed flowers mid-foraging trip, something honey bees seldom do.
Multicolored pollen baskets: This bumble bee changed flowers mid-foraging trip, something honey bees seldom do. © Rusty Burlew.

Comments

Granny Roberta in nw CT
Reply

What a great article on a subject I don’t see much about.

Still, I was a little disappointed when it didn’t turn out to be about all the different delicious varieties of pollen. I never find pollen to be bitter when I taste some that drops through the screened bottom board onto the underboard, UNLESS I’m careless about what other debris I pick up at the same time. Sometimes it tastes merely okay, but occasionally it’s been delightful.

So, if I knew you in real life I would be saying, well you’re just wrong then, aren’t you? But being polite to strangers I’ll say, no accounting for taste, and everybody’s allowed to be different.

And it was definitely a fascinating post.

Rusty
Reply

You are too funny, stranger. It might be scary to be your friend.

Keith Schultz
Reply

Hi Rusty,

Must be everyone’s taste buds are different. I like the taste of pollen in the comb. One of my favorites is when they 1/2 fill a cell with pollen, then finish it off with honey. I have a couple frames that have almost every cell filled with pollen I am adding to the super this year to make “comb” honey from. When I do cut and strain I cut the pollen out to put in a jar for my use. Pollen has every long and short chained amino acid. Biggest issue is the shell is difficult to digest. I think the pollen in combs is pre-digested from the enzymes and probiotics in the nectar coming from the foregut. Hmmm not even chocolate covered.

Keith

Rusty
Reply

Keith,

Interesting. I’m willing to give it a try.

Ken
Reply

When people ask me what pollen tastes like, I tell them dirt. If they want to ingest it, put it in something that will hide the taste.

Debbie in Ohio
Reply

You always have the most beautiful pictures!

Rusty
Reply

Thank you, Debbie!

pam winters
Reply

Very interesting material, particularly on honey bees, which we are working with now….we only have one hive and that’s fine….bees are so interesting!

Chris
Reply

I recently had some visitors who tasted some dark comb honey that had quite a bit of pollen – bee bread – mixed in it. One of them really liked it and she went back for several more tastes. The other tried politely to hide the repulsed expression it triggered. Maybe it’s like cilantro: some people experience it differently according to some genetic variant in their taste buds. I, myself, find it quite bitter but not terrible. Interesting article, beautiful photos, thank you!

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