Archives For pollinators

The surprising science behind hummingbirds and flowers

Do they have a “type,” or it is just economics?

Guest Blogger —  October 30, 2018 — 4 Comments

Fast and graceful, hummingbirds flit from flower to flower—but which ones and why? A Chicago Botanic Garden scientist and his collaborators recently made some unexpected findings on the subject.

It’s a common perception that plants are perfectly matched to their pollinators and that each pollinator has a specific flower type that they are attracted to. For hummingbirds, many gardeners and scientists alike have long assumed their flower type to be one that is strikingly red, tubular, and scentless.

Flowers that are often thought of as typical choices for hummingbirds:

Wyoming paintbrush (castilleja linariifolia)

Wyoming paintbrush
Castilleja linariifolia

Giant red paintbrush (castilleja miniata)

Giant red paintbrush
Castilleja miniata

Scarlet gilia (lpomopsis aggregata)

Scarlet gilia
Ipomopsis aggregata

It’s not hard to see why anyone might assume that hummingbirds and certain kinds of flowers are perfect matches. Hummingbird visits to flowers are visually striking, and many casual observations suggest a typical and consistent set of floral characteristics associated with this plant-pollinator interaction. The vibrant red or orange color of blooms appear as if they were designed specifically to attract the eye of hummingbirds. A hummingbird’s long bill appears perfectly matched for the extraction of nectar from the long, tubular flowers. But don’t be fooled—while it’s satisfying to organize flowers and pollinators and their interactions into clear-cut categories (known as pollination syndromes), these human constructs may mask what is really going on in nature.

Many “typical” hummingbird flowers belong to species that produce diluted nectar with lower sugar concentrations. Yet the hummingbird’s signature hovering flight burns massive amounts of calories. From the hummingbird’s perspective, it would therefore be much more efficient to drink from flowers with more concentrated nectars. Hummingbirds are also known to have acute color vision and show no innate preference for the color red—in other words, there is no reason for them to exclusively focus on red or orange flowers. And their long and slender bills are perfectly capable of extracting nectar from both long and shallow flowers. Finally, hummingbirds do have a sense of smell. So why would hummingbirds go out of their way to visit a limited selection of reddish, long-tubed, scentless flowers that produce cheaper nectar when they could feed from more suitable nearby sources in a diverse buffet of flowers?

Flowers that are “atypical,” or lacking the characteristics we associate with hummingbird-visited flowers (note that they vary in color, shape, odor, and nectar concentration):

Nuttall’s larkspur (delphinium nuttallianum)

Nuttall’s larkspur
Delphinium nuttallianum

Glacier lily (Erythronium grandiflorum)

Glacier lily
Erythronium grandiflorum

Ballhead waterleaf (Hydrophyllum capitatum)

Ballhead waterleaf
Hydrophyllum capitatum

The Garden’s  Paul CaraDonna, Ph.D., and his research collaborators Nickolas Waser, Ph.D., and Mary Price, Ph.D., of the Rocky Mountain Biological Laboratory, discovered that it all comes down to the basic economics that maximize energetic gain at minimal energetic cost. While camping and conducting research across the American Southwest, the three researchers kept observing something curious and unexpected: hummingbirds routinely visited flowers that lacked the expected typical characteristics of hummingbird flowers.

To make sense of these observations, the team dug back into their field notes from the past four decades and began to look more closely at the potential profitability of atypical vs. typical flowers for hummingbirds. Their field notes contained information on hummingbirds’ foraging rates at flowers and measurements of the nectar sugar concentrations; with this information, the team was able to calculate the energetic profits that could be gained by a hummingbird foraging at either type of flower.

How do hummingbirds choose flowers?

A broad-tailed hummingbird (Selasphorus platycercus) feeding from the so-called “atypical” flowers of pinedrops (Pterospora andromedea). Photo courtesy: Audrey Boag

What the team found was that typical and atypical flowers overlapped considerably in their energy content and profitability for hummingbirds. In other words, most typical flowers were no better than most atypical flowers and most atypical ones were no worse than most typical ones. Taken together, this research reveals that hummingbirds are making an energetic profit—not a mistake—when visiting these atypical flowers. In fact, atypical flowers may play a critical yet underappreciated role in supporting hummingbird migration, nesting, and populations in areas that seem to be lacking in suitable floral resources. The results of this research were recently published in the peer-reviewed scientific journal The American Naturalist. Neither typical nor atypical flowers are categorically better or worse than the other, and instead show considerable overlap in the energetic gain they offer to foraging hummingbirds.

Many hummingbird conservation efforts focus solely on typical flowers. Perhaps you have come across suggested hummingbird plant lists that are dominated by typical species. Now knowing that atypical plants can support the migration and residence of hummingbirds, we can consider more than just the typical plants as food resources in habitats and along migration routes.


Karen Wang

Guest blogger Karen Wang graduated with a B.S in ecology and evolutionary biology and a B.A in creative writing from the University of Arizona in 2017. She has worked as a research assistant on a variety of projects, mostly involving pollinators such as bees and moths. 


©2018 Chicago Botanic Garden and my.chicagobotanic.org

If you happened to walk around the Heritage Garden in late June, the unusual blue color of the Moroccan mountain eryngo (pronounced eh-RING-go), Eryngium variifolium, probably caught your eye, and its peculiar perfume tickled your nose. It was also swarming with flying insects.

The odor was not lovely and sweet. I would describe it as similar to musty, molding fruit—not unpleasant, but certainly not a fragrance you would wear. It only lasted a few days, during which time it hosted an amazing number and variety of insects. I attempted to photograph and identify as many of them as I could. This was a lot harder than I expected, because the insects were in constant motion and most of them were small. I didn’t always capture the key features needed to identify them at the species level. In spite of this, you’ll see that that the variety was astounding. Let me introduce you to what I found at the Chicago Botanic Garden recently.

1. Carpenter bee

PHOTO: a carpenter bee perched on a eryngo flower.

Carpenter bees are often confused with bumblebees because of similar size and coloring. The carpenter bee has a black abdomen and a black spot on the back of its thorax (middle section). That’s how to tell the difference.

2. Mason bee

PHOTO: a mason bee on an eryngo flower head.

Mason bees are in the Megachile family. The are also known as leaf-cutter bees.

PHOTO: a megachile bee is covered in pollen.

This mason bee has filled the “pollen baskets” on its hind legs with pollen from the eryngo, and they are now swollen and bright yellow. Pollen is also sticking to the hairs on its thorax and underside. It is a good pollinator!

Carpenter bees and Mason bees are native to our region. Honeybees are not native to the United States. I saw honeybees in the Heritage Garden, but they were not interested in this flower. Honeybees tend to go for sweeter-smelling flowers.

3. Red admiral butterfly

PHOTO: a Red Admiral butterfly is perched on a eryngo flowerhead.

The red admiral, with its characteristic red stripe across the middle of the upper wings, is  common in our area.

4. Azure butterfly

PHOTO: the azure butterfly's wings are smaller than that flower head it is perched upon.

This tiny gray-blue butterfly is an azure. Some azures are the same blue color as the eryngo flower.

A monarch butterfly also flew overhead while I was taking pictures, but it didn’t stop by. Again, the scent of this flower isn’t attractive to all pollinators. 

5. Squash vine borer (moth)

The squash vine borer larva can be a nuisance in a vegetable garden, but it is a beautiful and beneficial pollinator as an adult moth. Sometimes we have to resist the urge to judge our fellow creature as being good or bad. 

PHOTO: Picture of the moth perched on an eryngo flower head.

The squash vine borer was the flashiest visitor I saw on the flowers.

6.  Syrphid flies (hoverflies or flower flies)

When we think of flies, we tend to think of those annoying houseflies or other pests, but there are other kinds of flies. The Syrphidae family, also known as hoverflies or flower flies, feed on pollen and therefore serve as important pollinators for many plants. I found three species of syrphid flies on the eryngo.

PHOTO: flower fly hovers next to the flower head.

Flower flies resemble bees because of their yellow and black striped pattern, but this little insect bears the large eyes and short antennae that are characteristics of a fly.

PHOTO: flower fly on a leaf.

This syrphid is very small, only about a a quarter of an inch long. It looks a lot like the first, but it had a rounder abdomen. The pointed end is an ovipositor, so after inspection, I believe this is the female and the other may be male, so I counted them together.

7. Another kind of syrphid fly

PHOTO: syrphid fly on a eryngo flower

This syrphid fly is a little bigger and fuzzier than the previous one. It could easily be mistaken for a bee.

8. Mystery fly, possibly another syrphid

PHOTO: small black fly on a eryngo flower.

I was having a difficult time getting good picture of some of these small insects, and as a result, I didn’t get enough details to identify this half-inch-long fly with white triangles on the back of its abdomen.

9. Green bottle fly

Houseflies fall into the family of flies known scientifically as Calliphoridae, also called the blowfly family, and they were also represented on our eryngo plant.

PHOTO: green bottle fly seen from the back.

One view of this green bottle fly (genus Phormica) shows its iridescent green body.

PHOTO: Green bottle fly from the front.

The same green bottle fly can bee seen with its proboscis sipping nectar from the flower in this image.

10. Cluster fly

PHOTO: cluster fly on a flower.

This is the only image I got of another blowfly species, a cluster fly (genus Pollenia).

11. Tiger fly (I think)

Tiger flies prey on carpenter bees, which were feeding on the eryngo flowers, so seeing this predator around the eryngo makes sense.

PHOTO: a fly of some kind is perched on a leaf, partially hidden by the stem of the plant.

I could not get a good picture of this one, because it was hiding in the shadows under the flowers. The wing pattern suggests some kind of tiger fly. Its secretive behavior is also a clue to its identity.

12. Vespid wasp

The wasps I observed were far too busy collecting nectar and pollen to notice me. I had no concerns about being stung.

PHOTO: wasp perched on a eryngo flower.

Vespid wasps are a large family of wasps that include paper wasps—those insects that make the big paper nests. These insects live in colonies and they do sting when they feel threatened.

13. Black garden ant

I watched a few ants appear very determined as they walked up the stems of the eryngo, dipped their heads into the flower centers, and went back down the stem as swiftly as they arrived.

PHOTO: Ant on an eryngo.

The ants must have a colony living in the ground under the Eryngo.

14. Damselfly 

Where there are a lot of flying insects, there are going to be some predators. There were damselflies hovering over the blossoms, feeding on the flies, not the flower. 

PHOTO: bronze and blue damselfly perched on an Eryngo flower.

Damselflies are difficult to identify without getting a really good closeup of their abdomens and markings—and my picture wasn’t good enough. I believe this is some kind of spreadwing.

15. Assassin bug

Assassin bugs fall into the category of insects known as “true bugs.” I saw few assassin bugs lurking around the eryngo flowers.

PHOTO: an assassin bug hangs out at the bottom of the flower, probably about to catch another insect.

Assassin bugs and their kin have piercing mouth parts that penetrate their prey and suck the juices out. This guy wasn’t there to feed on nectar or pollen.

16. A spider web

Like the damselfly and assassin bug, this spider is hanging out somewhere under the flowers to prey on the flies, bees, and other insects that happen into its web.

PHOTO: Spider web that was underneath the flowers.

Spiders tend to set their traps and hide. I never saw the spider that made this tangle-web but I suspect it was well fed.

In total, I found two kinds of bees, two butterflies, one moth, six flies, one wasp, one ant, one damselfly, one assassin bug, and one spider—sixteen different bugs on this one bright, smelly plant!

The take-away from my experience is that scent is a really successful strategy for attracting pollinators. Like the titan arum, the Moroccan mountain eryngo produced a super potent blast of odor for a brief period time and then moved on to the next phase in its life cycle, which suggests that it requires a lot of a plant’s energy reserves, and may not be sustainable for a long time. This strategy works well  as long as the timing of the bloom coincides with the pollinators’ need to feed and ability to get to the flowers. 

I find this phenomenon fascinating. If you share my passion for plants and their relationships with insects, check out Budburst at budburst.org and find out how you can help scientists who need your observations to contribute data to their research. 


©2018 Chicago Botanic Garden and my.chicagobotanic.org

“The wonder of the world, the beauty and the power, the shapes of things, their colours, lights and shades—these I saw. Look ye also while life lasts.” —Anonymous lines found on an old tombstone in Cumberland, England

“While life lasts.” This can be a very brief moment in time for a spring ephemeral. In that narrow window that exists between thawing ground and the leafing out of the tree canopy, spring ephemerals—those woodland wildflowers that emerge, then quickly go dormant—live their life.

White trout lilies (Erythronium albidum)

White trout lilies (Erythronium albidum)

If you want to see some of the spring woodland flowers in bloom, you often have to be there on the day. In the McDonald Woods at the Chicago Botanic Garden, sometimes all you find are petals scattered on the ground, and you realize you have to wait another year. This is particularly true of species like bloodroot (Sanguinaria canadensis), whose blossoms only last for a day before they drop. Additionally frustrating is that cloud cover can hamper catching the full glory of the blooming of some species. You may show up on a sunny morning only to have the blossoms close up before your eyes. Species like spring beauties (Claytonia virginica) will only open in the full sun and will close again if clouds appear. This response to sunlight may be the result of temperature or light. Some ephemerals might provide longer viewing opportunities, since they hold their flowers for a longer period of time, or have many more plants that flower on different days.

Bloodroot (Sanguinaria canadensis)

Bloodroot (Sanguinaria canadensis)

Spring beauty (Claytonia virginica)

Spring beauty (Claytonia virginica) by Kaldari, via Wikimedia Commons

Most of the spring ephemerals are perennial. They have underground organs—bulbs, corymbs, etc.—that store nutrients to be used for producing leaves and flowers in succeeding year. White trout lilies (Erythronium albidum) are a good example. The trout lilies, both white and yellow species, derive one of their common names from the mottled leaves that some think resemble the markings on a trout. (Other common names include adder’s tongue and dog-toothed violet—the second name is curious because these are plants in the lily family, having no relationship to violets.)

Trout lilies also spread by underground rhizomes that form clumps, often covering large patches in the woodland, the mottled leaves camouflaging their abundance, only to become dazzling drifts of white when the sun appears. If you have  time, you can come out to the woodland early in the morning and watch the white petals of the trout lilies curl back and expose their yellow anthers to the sun—and pollinators.

There are also a few annual spring ephemerals. False mermaid (Floerkea proserpinacoides) is a spring ephemeral annual. Unlike many of the other ephemerals, false mermaid is inconspicuous in that it is a small, ferny green plant with tiny greenish flowers. Portions of the nature trail in the McDonald Woods are surrounded with acres of this species in spring. Even in these large numbers, without close inspection, it is difficult to tell when they are in flower. This species is dependent on its flowers producing one to three large seeds to be able to reproduce itself after the plant turns yellow and dies.

Many of the spring ephemerals depend on native bees for their pollination. 

The trout lilies are visited by an oligolectic bee (Andrena erythronii). “Oligolectic” means this is a bee that has a narrow, specialized pollen preference, typically for the pollen of a single genus of plants. The species name of this bee, erythronii, refers to the genus of the trout lily, Erythronium. Another ephemeral with an oligolectic bee pollinator is the spring beauty. The bee that is a specialist of this ephemeral, with its attractive pink-striped flowers, is Andreana erigeniae

Squirrel corn (Dicentra canadensis)

Squirrel corn (Dicentra canadensis) by Fritzflohrreynolds (Own work) [CC BY-SA 3.0], via Wikimedia Commons

While these plants often have specialist pollinators associated with them, they usually have several different pollinators that can visit, including other native bees and many species of flies.

For ephemerals in the genus Dicentra, such as Dutchman’s breeches and squirrel corn (Dicentra canadensis), queen bumblebees are an important pollinator. These ephemerals have tightly closed flowers, requiring significant strength to enter the flower and access the pollen and nectar. The large queen bumblebees are among the few pollinators equipped to gain access. This is not only important for the plants, it is also important for the bumblebees. Many native bees colonies die off in fall, leaving the queens to overwinter and start the new colonies in spring. These large, fuzzy bees are able to manufacture enough physiological heat, by vibrating their wing muscles and restricting their blood flow in the thorax, to get themselves flying early in spring before it’s warm enough for many other pollinators to go foraging for resources to start the new colonies. The spring ephemerals provide this important resource.

Besides being important sources of nectar and pollen for native insects, the spring ephemerals also serve the purpose of saving soil and reducing water runoff during a time of year when few other plants are growing.

Trout lilies, for example, have very efficient photosynthetic abilities and take advantage of the high light levels available in the spring woodland. This strong photosynthetic response requires large quantities of water to maintain the process. Therefore, abundant populations of this species and other ephemerals absorb large quantities of water that would otherwise move off site, often carrying valuable nutrients and soil with it. This high demand for moisture also causes the ephemerals to have shorter flowering periods in times of drought. In your yard, you can encourage ephemerals to flower longer during dry conditions by providing a little extra water. There is also some thought that the rapidly decomposing foliage of these “short-lived” plants provides readily available nutrients for other plants that begin growing later in the season.

One other fascinating thing about spring ephemerals is that essentially all of them rely on ants to disperse their seeds. This relationship is referred to as myrmecochory—”myrmex” being the Greek word for ant.

Each seed of the spring ephemerals has a structure called an elaiosome attached to its surface that attracts ants. The elaiosome is rich in lipids and proteins. The ants take the seeds back to their nests and consume the elaiosome as food, after which they bring the seed to the surface and deposit it on their trash piles, where the seeds tend to germinate in a rich, organic seedbed.

I include another plant with elaiosomes in the list of spring ephemerals. This is parasol sedge (Carex umbellata). This grass-like, early-flowering sedge produces most of its seeds very close to the soil surface, where ants are more likely to find them. It is not uncommon to find ants nesting at the base of these plants. I often get questions from people who have planted ephemerals in their yard, but say they don’t see seedlings, while their neighbors are finding them on their property. It is more than likely that the neighbors have the ant colony that is harvesting the seed and sowing them at the neighbors’.

Parasol sedge (Carex umbellata)

Parasol sedge (Carex umbellata)

Given that the spring ephemerals are adapted to growing in a cool, moist environment and highly dependent on early spring pollinators, climate change is likely to cause stress in the system. Early warming and possibly drought conditions in spring may disrupt pollinator interactions or shorten flowering periods, making seed production more difficult, or reducing the amount of time ephemerals have for storing nutrients for future flowering. 

False rue anemone (Isopyrum biternatum)

False rue anemone (Isopyrum biternatum)

With spring on the horizon, you should make plans to visit the McDonald Woods to view the diversity of colorful spring wildflowers. For those of you taking pictures, pay attention to weather forecasts, and be mindful of the potential to damage other vegetation while attempting to get the perfect shot.


©2018 Chicago Botanic Garden and my.chicagobotanic.org

In recent years, the plight of pollinators has gotten a lot of press, and rightly so.

I spoke with the editorial board of the Chicago Tribune when they were investigating the well-intentioned distribution by General Mills of “one size fits all” wildflower seed packets to combat the declining populations of bees and other pollinators. 

The decline of pollinator populations is well documented around the globe. Much attention has focused on honeybees, which are extremely important agricultural pollinators, but many of our native bees are vastly more imperiled. For example, the rusty patched bumblebee, native to the Upper Midwest, was just listed this month by the U.S. Fish and Wildlife Service as endangered.

A rusty-patched bumblebee on Culver’s root in the UW–Madison Arboretum. Photo by Susan Day, UW-Madison Arboretum.

A rusty-patched bumblebee working on Culver’s root in the University of Wisconsin–Madison arboretum. Photo by Susan Day, UW-Madison Arboretum.

Many people are concerned about these losses and asking what they can do to help support bees, butterflies, and other pollinators. For a start, it’s more beneficial to pollinators to plant species that are native to your region, and perennial. Here are five more pollinator-friendly actions that everyone can take.

  1. Provide resources: For pollinators, this means flowering plants with pollen and/or nectar. Diversity is key, as flowers of different colors and shapes will attract different pollinators. Be sure to provide resources across the entire growing season, so include species that bloom in spring, summer, and fall. Regional native plants are the species our local pollinators evolved with, so they recognize and use them…and you don’t have to worry that they will become invasive!
  2. Provide host plants: The larvae of many butterflies and moths have particular species that they need to eat to develop, as monarchs need milkweed. Providing host plants will ensure that the next generation of butterflies can mature. Just be willing to accept hungry caterpillars eating those plants.
  3. Provide nesting sites: Many insects like to nest in bare ground, hollow stems, or leaf litter. Allowing your yard to be a little less tidy can benefit insects. Many attractive bee houses are available for sale, and do-it-yourself instructions can be found on the web.
  4. Avoid pesticides: Pesticides are designed to kill insects, but sometimes they also kill pollinators unintentionally. Systemic pesticides can persist in plants for long periods of time and are present in all parts of the plant, including nectar and pollen. So if you choose plants for a pollinator garden, make sure they haven’t been treated with systemic pesticides. If possible, make your entire yard pesticide-free.
  5. Learn more about pollinators: There are some great resources on the web—including those created by the Pollinator Partnership and the Xerces Society—that can help you do even more for pollinators.

Help for pollinators begins in your own backyard. These native plants below are recommended to bring back pollinator populations. (Don’t overlook trees—native maples and willows can provide critical resources early in the season.)

Beebalm or bergamot (Monarda fistulosa)

Beebalm, or bergamot (Monarda fistulosa)

New England aster (Symphyotrichum novae-angliae)

New England aster (Symphyotrichum novae-angliae)

Stiff goldenrod (Oligoneuron rigidum)

Stiff goldenrod (Oligoneuron rigidum)

Prairie blazing star (Liatris spicata)

Prairie blazing star (Liatris spicata)

American pussy willow (Salix discolor)

American pussy willow (Salix discolor)

Purple coneflower (Echinacea purpurea)

Purple coneflower (Echinacea purpurea)


Read more about the science behind this important topic in the Natural Areas Journal article, The Importance of Phenological Diversity in Seed Mixes for Pollinator Restoration by Kayri Havens and Pati Vitt, Chicago Botanic Garden.


©2017 Chicago Botanic Garden and my.chicagobotanic.org

PHOTO: Pollinator infographic.